"These are beech trees(Fagus). The larger one has advanced beech bark disease. When this happens beach trees propagate from their root system due to the stress. This new tree (the smaller one on the left) became mature before the parent tree died. Once the branches from the new tree grew into contact with the main trunk of the parent tree, the rubbing action would create a wound on trunk and branch where contact is made. Beech has thin bark and bc these trees are probably genetically identical their cambium layers could easily fuse at the wound site creating a kind of graft. Both trees (really just a single tree actually) now pass water and nutrients back and forth through these fused sites. Really neat and while uncommon not extremely rare for this species."