DdRT - (not to be confused with a double rope technique (drt), a rock climber's term when using two independent ropes at one time.)
Tree climbing's doubled rope technique is unlike most other rope-assisted activities in that you use a loop of rope to both ascend and descend.
A single rope, draped over a tree limb and connected as a loop using a friction serving component (hitch or lockjack) to adjust the loop larger or smaller is used to create friction upon itself, without mechanical assistance, for both climbing up a tree and coming back down again.
This self-belaying method uses the rope's own end to both secure the climber during ascent as well as control descent. Essentially, you make an adjustable loop, which is made longer or shorter to move in or out and up or down in the tree.
Once in the tree, it's essential for you to learn the techniques to help guard against personal injury – and to develop skills for strategizing where you want to go and what you want to do when you get there.
These include using positioning lanyards wherever possible, but especially when you are resting with acute angle in lifeline or redirecting the lifeline. It is also useful to use a redirect to guard against slamming into the tree trunk in case of a fall. Double-crotching uses the rope's opposite end or a second rope to enhance balance, which is especially helpful when performing a task like pruning a dead limb. Finally, descent should be done slowly, to avoid burning the tail section of your rope.