This is how I did it;
PART A (Using CE Lightning to 'Grow a Tree')
1) Create a new 720 x 480 (or whatever you choose) composition and name this 'tree'
2) Create a new layer (same size as the comp) and select absolute black (as an alpha channel) as the color
3) Select the layer, name it branches, and apply CE Lightning to it.
4) In the CE Lightning Effect Window, set the origin point somewhere near the bottom (I chose 348,442), and the direction point slightly above it (I chose 356,330). Varying these settings will change the shape, size, and branching of the tree. Set the 'Lightning Type' to 'Breaking'.
5) Set 'Conductivity State' to '50', 'Core Radius' to '15', 'Core Opacity' to '100%', and 'Core Color' to 'White'
6) Set 'Glow Opacity' to '0', and 'Alpha Obstacle' to '0'
7) Set 'Forking' to '100%', and select the 'Decay Main Core' checkbox.
8) Adjust the 'Turbulence' and 'Decay' Controls until you get a basic tree shape you like. I chose a 'Turbulence' setting of '0.86', and 'Decay' to '0.4'. At this point, you can also fine tune the 'CE Lightning' effects 'origin' and 'direction' settings to change the shape and size of the tree as desired. Play with all four settings to get the tree exactly how you want it, as once you begin to make the leaves grow these settings cannot be altered.
You should now have a tree that looks something like this.
9) Move the time ahead to the point at which you want the tree to 'finish' growing and set a keyframe for the 'Decay' control.
10) Move the time marker back to a point in the timeline where you want the tree to start growing and change the 'Decay' setting to a sufficiently high number to cause the tree to become a small 'bud'. I used a setting of '10'
11) Preview the animation and set additional keyframes that will cause the tree to grow in a smooth rate. Select all keyframes and apply 'easy ease in', (layer>keyframe assistant>easy ease in) Preview the animation and fine tune settings to taste.
12) Apply the 'Ramp' filter (effect>render>ramp) and set the start point, end point, start color, and end color to give the tree a color and shading that is pleasing.
13) Apply the 'Bevel Alpha' filter (effect>perspective>bevel alpha), and adjust settings to give a 3 dimensional look to the tree. Preview the Animation and make any adjustments to fine tune the tree.
You should now have a tree that looks something like this
PART B (Using After Effects to create the "leaves.mov'')
1) The first thing we need to do is to make the leaves movie that will be used by 'foam' to grow them on the tree. Create a new composition (360x240 or smaller) and name it leaves.
2) Create a new layer (same size as comp), green in color, and name it 'leaves element'.
3) Using the pen tool, draw a cluster of leaves, so that you have something like this
4) In the timeline open the 'leaves element' layer and then open the masks group. Move ahead in the time line to a point where you want the leaves to 'finish' growing. Make a keyframe for 'mask shape'.
5) Move the time marker back in the timeline to a point where you want the leaves to 'start' growing. Using the pen selection tool, reshape the leaves to create a beginning leaf shape. Don't worry about trying to make the beginning or finish shapes too small, as we're going to resize them later.
You should now have some leaves that looks something like this (layer window)
6) Apply 'CE Roughen Edges' to the layer, and set the 'Edge Type' to 'Cerox Color'. Set the 'Edge Color' to a color that enhances the effect (I chose 'yellow'). Set Border, and Edge Sharpness to taste.
7) In the Time line Move to a point where the leaves finish growing. Scale the leaves to taste, and set a keyframe. Set a Rotation angle that is pleasing and make a keyframe for that.
You should now have some leaves that looks something like this (comp window) when they are finished growing
8) Move the time marker back to where the leaves start to grow. Adjust the scale and rotation, so that when previewed the leaves grow and rotate in a way that is pleasing.
9) Duplicate the layer three or four times. Adjust the layer 'scale', and 'rotation' , both for start and finish keyframes to taste. The Rotation (amount and direction) and scale should vary from layer to layer to keep a more natural look to the animation. Stagger the Start and Finish keyframes in each layer (but keep scale and rotation keyframes sync'd in each layer) in a fashion that is pleasing and natural. Preview and fine tune.
You should now have a cluster of leaves that looks something like this (comp window) when they are finished growing
10) Make a movie of the 'leaves' comp, and name it leaves.mov. Make sure that the comp is sufficiently long to remain visible throughout the finished 'growing tree' animation. In other words, the leaves, will stay in their finished state for a period of sufficient duration to remain visible to the end of the finished project.
PART C (Using Atomic Powers' Evolution 'Foam' to grow the leaves on the tree)
1) Create a new comp (same size as the 'tree' comp) and name it branches only. Drag the 'tree' comp into the timeline.
2) Double click on the tree comp to open it in the layer window. Using the 'pen' tool, draw a mask around each of the areas that you want leaves to grow in.
It should look something like this
3) With the layer window active select all the masks by either dragging a box around them or by using keystrokes (command+A). Then copy them to the clipboard (edit>copy) or (command+C).
4) Create a new layer (same size as comp), white in color, and name it 'white'.
5) Create a new layer (same size as comp), black in color, and name it 'black'.
6) Select the 'black' layer and apply the 'Ramp' (Effect>Render>Ramp) effect to it. Set 'Ramp Shape' to 'Radial Ramp'. The start color to 20% grey, the end color to black, the start point in the middle of the tree where you want the leaves to be, and the end point near one of the edges of the layer, to create a dark grey radial gradient emanating out from the center of the tree crown.
7) With the 'black' layer still selected, paste the masks from the clipboard (edit>paste) or (command+V), into the black layer. Apply a Fast Blur to the black layer (Effect>Blur & Sharpen>Fast Blur), and set the 'Blurriness' to about 20, with the 'Blur Dimensions' set to 'Horizontal and Vertical'.
8) In the timeline, turn off the visibility of the 'tree' layer (the 'eye' icon).
You should now have something that looks like this
9) Render a frame (Composition>Save Frame As>File>, name it 'flow map', and import it back into the project. This will be used as a flow map to tell 'Foam' what direction to grow leaves, and where to stop growing them.
10) Create a new comp and name it 'Tree with leaves'. Drag the 'tree' comp into the timeline of the new comp.
11) Drag the 'flow map' into the new composition.
12) Move the Time Marker (in the timeline) to the point where the tree has finished growing and the leaves are to begin appearing. Create a new Layer (same size as comp), and apply Evolution 'Foam' (Effects>Evolution>Foam> to it. In the effects window set 'View' to 'Rendered', then select the producer point icon (cross hairs should appear in the comp window), and click in one of the black areas of the 'flow map' closer to the trunk of the tree. Set the 'Wind Direction' (Physics>Wind Direction) to point to the other end of the same black area (pointing away from the tree trunk).
13) Use the following settings in the effect window (you can adjust them to your own taste later) as a starting point.
Wind Speed (Physics>WindSpeed> to 0.150
Lifespan (Bubbles>Lifespan) to 1000
Rendering>Bubble Texture to 'User Defined'
Rendering>Bubble Texture Layer to 'leaves.mov'
Turbulence, Wobble Amount, Repulsion, and Pop Velocity (All in the Physics area) to 0.000
Viscosity and Stickiness (Both in the Physics Area) to 4.000
Select the 'flow map' layer as the 'Flow Map' (Flow Map>Flow Map>Flow Map)
'Flow Map Steepness' to 0.000
'Flow Map Fits' to 'screen'
All other settings should remain as default.
14) Turn off the visibility of the flow map layer (in the timeline), and preview the animation.
15) If that particular area looks good, duplicate the previous layer enough times to provide a separate layer for each of the black areas in the flow map. Turn the 'flow map' visibility back on, and in the effects window for each layer, set the 'Producer Point' in a different black area of the flow map, and readjust the 'Wind Direction' control for that particular black area. Do this for each and every layer until every black area has it's own 'producer point' and 'wind direction' setting.
16) I created an additional duplicate of the 'foam' enabled layers and set it's flow map control to none, and readjusted everything so that there was a general growth throughout the whole tree crown. This required setting things up so that there was some repulsion between the leaves.
17) Turn the 'flow Map' visibility back off (in the timeline), preview the animation, and make any final adjustments.
You should now have a tree that looks something like this
PART D (Putting it all together)
1) Create a new comp (same size as the 'tree' comp, and name it 'Final Comp'
2) Create a new layer (same size as comp), black in color, and name it 'Background'. Apply the 'Ramp' (Effects>Render>Ramp) to this layer, and set it up so that it ramps from a light grey on the bottom of the layer to a dark grey at the top.
3) Drag the 'tree with leaves' comp into the timeline and duplicate it. Rename the duplicate as 'Tree Shadow'.
4) Select the 'Tree Shadow' layer and apply 'CE Radial Shadow' effect (Effect>Cult Effects>Radial Shadow) to it.
5) In the effects window, use the default settings for 'CE Radial Shadow', except turn off (uncheck) the 'Composite Shadow' Setting.
6) Apply the 'Corner Pin' (Effect>Distort>Corner Pin) effect to the 'Tree Shadow' layer, and adjust to give the effect that the background layer is the ground or 'earth' that the tree is growing out of, and that the light source is casting a shadow of the tree on the ground.
7) Save the project and output it in the format of you choice.
Phew, that was a long one.
---Mark Simpson is a leader and frequent contributor in the Adobe After Effects COW.