Step 2: Getting them on
The easiest way to get the people to comply is to bet them (in the army you just put a gun to their head). They will go along with this if they think they can win something. (even if it is just to try to prove you wrong).
They need to be in a position like they are sitting on an invisible chair, holding the tree to keep themselves upright, knees at 90 degrees and with the tree between their legs.
Now you take one leg (does not matter which but Ill say left to keep things clear) and turn it so the left ankle is behind the knee of the right leg.
Next take the right foot, pull it back under their butt and let them slide down the tree, point the toes of the right foot to the left and keep it under the butt as much as possible.
A gentle push on the shoulders makes sure they are all the way down.