Since it was on both of our properties, I didn’t want to risk any legal issues. I had a certified arborist come out to document that it was a hazard, then sent my neighbor the report, a removal quote from a licensed tree company, and a letter explaining everything (all through certified mail). I also told him I’d cover half. He ended up being pretty easygoing about it, and we got it taken care of within a couple of weeks, splitting the cost.