I can't put collisions on the trees

I’m working on a project where the map is a big forest, I created this forest with the option “add trees” to the ground, once I click on “tree collision” but no collisions are triggered and I do not know how to do because the trees are many and I can not collide one by one, Help me …

Don’t add colliders to the scene.
…add a collider component to your tree prefab model(s). I would typically add a capsule collider and position it to match the trunk, or maybe also one or two more simple colliders ( capsule or boxes) for large low branches.
Then when you paint the trees onto the unity terrain… all trees will have the same colliders already,