Adding colliders to trees

To add a collider I selected the tree went to the component menu then to physics and to the collider depending on what shape you require.










A collider will be added as a green outline to the object. This can be resized using the menu to the right. The width, height and position can be changed.









One the collider has been placed, create a prefab, add the tree to the prefab and click apply. You now have a collider to all the trees in this prefab.