How to create trees with working mesh colliders ?

Hello, I recently started a new game, and I have the following problem : I created all the 3D world, I have finished the scene where the action takes place (I put all trees, buildings, etc. whatever is necesary in my scene) but I have a problem : The player and other objects can pass through trees because they can not detect collisions. I searched the internet and found the solution is to put a capsule collider, and this has proven to work very well but the problem is that the game is a shooter and capsule collider is not following the exact shape of the tree. So when I shoot the tree the bullet holes appear to float in the air and when I try to pass quite close to a tree you cand see the collider is not exactly as the tree and you collide a little bit further than the tree location. So a MESH Collider would be ideal, but is not working ...... So what can I do to get the desired effects ? How can I solve this problem ? [sorry for any language mistakes I don't speak English very well]