If you're hanging out in a tree stand, there's no need for a gun. I've heard of people taking sticks up in the trees to whack at bears that are trying to climb up them, and that usually fends them off. Especially when they connect with a blow to the noggen.
I don't use backup on spot and stalk either, but that's a whole different story.

Good luck on your first bear hunt! I'll be out in May chasing the blackies in south east Alaska. Can't wait!