Here are two birch tree models, complete with collision meshes and also ready for pagedgeometry. They are reasonably low-poly, don't use them like grass though They do perform pretty well though considering. Further info in the readme file.
I hope you find a use for them
All textures and models were created by me, you have my permission to edit any of the included files, use and release them for free Rigs of Rods projects provided you credit me, LJFHutch.
On the repo now.