What bargain does Billy make with Little Ann and Old Dann when they are finally ready to go coon hunting? What happens as a result of this promise?

From the text:

"'I thought about that, Papa,' I said, 'but I made a bargain with my dogs. I told them that if they would put one in a tree, I'd do the rest. Well, they fulfilled their part of the bargain. Now it's up to me to do my part, and I'm going to, Papa. I'm going to cut it down. I don't care if it takes me a year.'" Chapter 8, pg. 80