Its not a bad idea but you do trade one problem for one or two others. The branches will not match from the other side which can look strange as you pass by. Also the tree objects will have quite a few more vertices and faces in them. I prefer to stick with double sided materials on flat planes and I use 2 or 3 similar tree textures for each tree. They can be photos of the same tree from different angles, photos of different but similar looking trees, or 'photoshopped' variations of the same tree. I did use a combination of both these methods for a number of trees in the Eastern Creek Laser track, however they were a 3 pointed star shape and suited the spindly gum trees of that track.
Also please note that the linked article included incorrect information:
"rFactor will only ever show the front of a face, and the same is generally true of all other 3D games"
This is not true. You simply specify the material as either double sided or single sided and all objects with that material will appear either double sided or single sided respectively. Trees generally work best as double sided and with 'pointy' normals (or 'upnormals' in 3DSimEd - basically they point straight up so that both the front and back faces are lit evenly by the diffuse light).
