I see signs of a lot of different insect activity in your photo. In a situation like this, it can be really difficult to identify on primary cause of the tree's decline. There is an insect called the flatheaded appletree borer, that may have created some of the holes in the trunk, and that can damage the cambium to such an extent as to kill a tree. You can read more about appletree borer here: https://www.canr.msu.edu/ipm/diseases/flatheaded_appletree_borer?language_id=

Without knowing more about the tree's history and overall health, there is not much more that I can tell you. If you can provide more information I might be able to help more. How old is the tree? Are there limbs that are healthy and show no signs of damage? Photos of the entire tree might be helpful.