Only rigidbody on half of my trees

so, im new at unity, and used the tree function which comes with the terrain. i downloaded a few tree models, but only half of them had rigidbody which means that i can move through half of my trees. i tried to put a rigidbody on the terrain, but i just fell through regardless of how high i put the fps controller. How can i make all my trees interact with physics?

Rigidbody is to enable things to have physics and fall, you need a collider. Try putting a Mesh Collider on all the trees.