You have to have installed ATree3D script for 3D Max. After this you have to unzip downloaded presets (archive from 3dtreexchange), and find there (in archive) At3d file. Open ATree3D in 3DMax and find LOAD button to load preset. Than press BUILD TREE and voila - new buch ready to render!
Most importat info - ATree3D is free and ready for commercial use, my plants presets too:)