For me, it was advancing the top tether while balancing on the foot tether. Different tree types and diameters change things. I think some of the guys who've made videos that make it look like walking up a tree (North Fourty and Scott Adkins come to mind) is so easy, you have to pay real close attention to the details. I think some of the details matter. Like Scott Adkins has his foot loop on one side of the tree and the other looped the opposite direction. Length of bridge, distance between foot tether top and foot, distance between top tether and bridge. There seems to be lots of details that make it easier, but are taken for granted. And, then you throw in the different tether types, foot loop types, bridge types, connection points, etc; it all gets overwhelming. I'm getting a lot better at it, but only after watching the littlest details in some of the videos. I've watched Scott Adkins videos over and over making mental notes of tether height compared to forehead, distance between steps, and move distances.