Hi,
I just tried it out and finally got a nice .mdl tree

The .obj export works for me perfectly, including uv map, if you put the texture files into the same folder as the .obj and .mtl file. Check .mtl for file name. What you need to do manually: go in MED to Manage Skins -> Skin Settings -> check Texture -> Texture file -> check External -> select corresponding .png texture file (or import from Skin Editor). You have to do it only twice for the 2 textures (bark and leaves).

The .x export makes a very large file, moreover the resulting .mdl is incorrect.

One trick to decrease poly count: use .png texture instead of leaves just like in TreeMagikG3:
at Leaf tab uncheck all the 4 checkboxes on top (removes high poly leaves), and at Branch tab check all the 6 checkboxes on top (Cross Horiz. & Vert. Geometry adds the leaf textures).
But a nice tree is still over 1000 poly... Maybe some more playing is needed

And an interesting thing: both TreeMagikG3 and Tree[d] have the same icon...

And nother useful tool is included:
If you want to use LOD stages, you can export it as a billboard (sprite) in .png or .tga format. And you can it put onto a simple 2 triangle mesh in MED to make a .mdl. But better to use a 2 sided mesh, or even better to use a 2 sided crossed plane mesh. If you need it you can use my tree models from my MapBuiilder demo: http://mapbuilder.zxq.net

I hope it helps