So the other day I was mowing like a I usually do and I notice a hole in my
tree that I honestly have not noticed before. I'm pretty sure this hole
looks like it has been there for a while, but I wanted to know if it
something that will kill the tree soon and if so, is there anything I can do
about it.

Also, I took pictures of the hole and also got the camera inside the hole, I
wanted to find out, in the last picture, is that a squirrel in there?

http://www.chopinsociety.com/tree.htm

Should I be worried about anything or just let the hole and its inhabitants
be?

Gene