This is a paid asset, but now you can download it totally free. However, please keep in mind that this package is only provided for studying or testing the product prior to purchasing it, not for business functions.
Overview :
This pack contains 20 mountain trees (60 including all LOD stages). Textures for the trees are combined into three atlas textures. This way, you will save a lot of draw calls (a scene with all 20 trees renders with only 44 draw calls in Unity).