Tree callus

I spotted a large mass on a tree and am listing it as a tree callus or tree wound. At first I thought it was some type of nest but upon closer inspection, it is part of the tree so it is a tree callus. Trees do not heal, they seal. The tree covers the opening by forming specialized “callus” tissue around the edges of the wound. After wounding, new wood growing around the wound forms a protective boundary preventing the infection or decay from spreading into the new tissue.