I'm not exactly sure about the trees, but I do know a few utilites and L-systems for creating trees that may come in handy. If all you need is an image that you can duplicate and rotate 90 degrees, in order to make trees for AH, then I can help. In fact, the sky is the limit as to the variety you could create.
Plant Studio (Free) is available at:
http://www.kurtz-fernhout.com/The other method I use most often requires Pov-Ray and yes the trees it makes are very, very nice. The following site includes work of a true Pov-Ray master, Giles Tran (yes, he's French I believe).
http://www.oyonale.com/There is a macro for creating trees AND grass with Pov-Ray on his site. Magnificent! Check out some of the other tree/grass web links there as well.