Just a quick idea. You can create a tree trunk, then a small arc that will reflect the curve of the tree top, add a particle folder and put some leaves and branches, use the Crashcore 'Copy Curve' and 'Paste to Layer Translation' and play the animation stopping it when the tree looks good. Then save as png and you have a quick tree. I would use a size twice as big as you anticipate using so you can insure the best quality when it is rasterized.
You can reuse this moho file over and over to generate more trees or bushes with slight variations. This is a quick test but with some thought I think it would be possible to create some nice bush and tree generators you can use over and over.
I went home and did a few more quick tries during my lunch break and uploaded them - of course I forgot to include the original mentioned in the post. :/ I'll add that one later. This zip just shows two simple examples without using the animation.
Here is a screen of each (ain't pretty, just shows the concept).