I like to climb trees. It grew out of geocaching, when I found that I was particularly interested in caches that were hard to get to, and then that narrowed down to those that were as high off of the ground as possible. After 4,000 geocache finds I thought it was time to stop, for fear of developing an uncontrollable addiction... but the tree-climbing bug had bitten. Now I am all over it. Trees are all unique, and climbing them differs significantly from rock-climbing in terms of being more three-dimensional, and in terms of a particular tree climb often never having been climbed by a human before. And they are often ancient. And beautiful. And the views from the top are usually tremendous.
In the absence of any UK clubs for recreational tree climbers, I set up and administered Recreational Tree Climbing UK on Facebook. It is still going, so join! We have annual (or more) "Sleepover" weekends in Southampton where we sleep in trees and muck about with each other's gear.
Since there was very little in the way of information about technical tree-climbing, I put together a series of videos, in a somewhat piecemeal fashion, to fill that gap since people in the group were often asking. It is easier to demonstrate than explain, though the strong caveat that I don't know what I'm talking about and that Google and YouTube are no substitute for formal training from a qualified practitioner definitely applies!