I would get a saw instead of an ax. I'll tell you what happened to one of my friends. He was out in the boundary waters and a tree fell on top of him and landed on his pack. He was basically pinned underneath the tree with just enough breathing room to grab his saw. Slowly he sawed away at the trunk until he got out. He said he would never have been able to do it with an ax.

Never camp near dead trees. We call these widowmakers.