This is a paid asset, but now you can download Low Poly Forest Pack Free.
Detail this asset from Unity Store: Original Link
Low Poly Forest Pack v1.1 (Latest version)
“If possible, please buy the package to support the developer”
Every tree you need to populate a massive forest! Each tree has a proper pivot point for perfect planting. Each has it’s own capsule collider for the trunk and canopy for low overhead collision data. Assets use a simple vertex color mobile shader, no complex overhead of other tree shaders. Ideal for flight sims, RTS or MMO games.
Each tree asset is 28 – 36 triangles in polygon count.
Textures are 512px x 512px and use minimal draw calls.