How to use my tree model and mass place them on a terrain

So i made this great low poly tree in blender, imported it over to unity but now i can place it by hand into the scene but i cant mass place it on terrain. So does any1 have a solution(try not to link to other posts because ive spent a solid 6 hours searching them i just want a solution to this specific problem) The only thing i can come up with is that its something to do with the meshes or something? Idk.

EDIT: Ok now i can place it because i forgot to make the whole model one thing in blender but whenever i place it it places sideways help? Also if you are far enough away they render really shrunken and small. Ok now i got a script to fix it but it distorts the models so i still need an answer for the original question. Also making it into a prefab doesnt help cuz i cant mess with rotations, its default set at x 277 or something

Youll want to turn it into a prefab first. Set its rotation in the prefab first. then drag it into the tree slot in the terrain editor