treed(d) ( http://www.frecle.net/index.php?show=treed.about ) exports very nice animated trees, however it's not very lowpoly unless you do some adjustments
You also need to resave the mesh in Fragmotion or similar to get the root frame if you want the animations.

This is how I do it :

1. Make a tree
2. Go the branch Tab
    Set 10 branches (not sure how many bones rad support)
    Check Cross Horiz and Vertical (all of them)
    Subdiviosn : Adapt from trunk.
3. Export as DirectX mesh (also get the textures from the texture folder where tree(d) is installed)
4. Load in Fragmotion and reexport, check Add Root Frame and Hierarcial Mesh
5. import to rad.

wow, the thing with resave helped me now, when I export gMax animation to one x file! gooood!!!
thanx! no more list of separate x files!!!