Why can't I mass place solid trees?

I’ve made a prefab of an existing tree and added a mesh collider.
It works well when I drag and drop it into the world, but when I so much as try to paint it on to the terrain or mass place, they’re tiny and you can walk through them.

I’d prefer to keep a mesh collider instead of a capsule or box collider (for that “close shave” kind of feel.)

Any suggestions?
Also, any suggestions on how to make nice, sexy mountains would be appreciated.

Sounds like you dont have “add tree colliders” from terrain options selected. That button apply tree prefabs colliders to trees in terrain.

I have “Add tree colliders” in the terrain options selected.
And I have a capsule collider and edited prefab of the tree. They’re still not the
right size and you can walk through them. You can see in the pictures below.
I have not gone over the collider limit in the scene.

Dude Use a mesh collider, and then find the 3d mesh of your tree and drag it into the mesh collider on the tree in the scene.
Mesh colliders become exactly the shape of the tree and fit it perfectly.

I think antony answered the other part of the question perfectly.