This is one I made earlier this year. This was the first climb in several months so I was rusty and I was wearing shorts with no knee pads so forgive the climb.
I think the biggest problem people have trying this is to overcomplicate it. I was guilty if this when I started. All you need are two things aside from your saddle. The first is your regular top tether. The second is a foot tether. The simplest foot tether is just a rope with a loop tied on one end and a second loop tied with a Blake's hitch for adjustability on the other end. Forget about the Distel hitch and the carabiner in the photo. That can come later.
Pick a basketball diameter straight limbless tree. There is no need to make life harder on yourself when you are learning the baby steps.
Imagine you are sitting on a couch and there is a length of climbing rope attached to a pole in front of you. If you can stand up off the couch on one foot while pulling yourself up with the rope simultaneously then you can 2TC.
Put your top tether on the tree about level with the top of your head. Put the foot tether on the tree under it about 4 inches. Clip your saddle into the top tether and adjust the lead to where you can sit down comfortably in the saddle as if you were going to just hunt at ground level. Adjust the foot tether to a height where you can comfortably step up into it. Now, with your feet on the ground, take one foot (I use my left) and step up into the loop and at the same time hold onto the top tether lead and pull yourself up. Your other leg will now go to the side of the tree. If you did this right, you will be standing in the foot loop with your body near the tree. Now reverse that move and step back down. Do this move several times up and down to get the feel of it.
Once you are comfortable with that, repeat the move but at the standing in the loop position you will loosen the top tether and move it up about 18 inches. Keep your fingers out from under the loop. Cinch down the top tether around the tree and slowly sit back in your saddle.
Now take your foot out of the foot loop and move it up about 4 inches under the top tether. Put your foot in the foot tether and stand up as usual. Now sit back down. All you would have to do now is move the top tether up again but don't.
Sit back down and move the foot tether back down the tree about 18 inches so that you can now step into it and relieve tension on the top tether. Move the top tether down and sit back in it. You should be back on the ground.
I would just practice this set of moves up and down the tree one or two moves for a while until you are really comfortable. Once you get these moves down you can go as high as you want by simple repeating the moves.
I think it is very important to learn the moves close to the ground at first and practice on an easy tree.