When I was younger and still had a nice tail, I could climb branchless trees with just a piece of rope with loops on each end. We made some metal tree crotch wedging saddles that could be adjusted for length that had spikes that would firmly bite into the crotch of a tree. We have a lot of trees that form a crotch about ten to 15 feet up. These were handy because it allowed for some elbow room up there. Then we all got lazy and made rope/wood steps to get to the crotch stands a bit easier. Someone came along and stole the whole works.