Adjusting normals for two meshes that intersect

Let's say I have a tree trunk as one object, and a branch as another, separate object that is placed onto the side of the trunk, but a portion of the mesh is inside the trunk. Both the trunk and branch can grow at separately and be placed differently, thus they can't be in a single mesh as far as I have thought out.

To make this look natural, I need to adjust the normals in the area where the two meshes intersect. How is this possible in unity?

(PS: I know about the tree generator, I'd like to make my own)