When we are growing trees to send out to our research partners, or for study in our research nursery, we are looking to set a permanent canopy at around 12 feet. With the conditions most trees are growing in, they would be shrubby and around 7 feet tall. To get them higher, and keep them straight, we have a lot of methods, like pruning, staking, and tree therapy.
Tree therapy isn't really an official term. It is simply the bending of trees to get them to develop caliper and grow in the direction we would like them to. When you bend a young tree, you can almost feel the fibers inside of it breaking. When a tree bends and moves, it responds by growing stronger, similar to human muscles after exercise. This also occurs naturally, from the blowing of the wind. This response is called "thigmotropism," which I talked about earlier in relation to staking.
Tree therapy can be a tricky thing. If you bend too lightly, you aren't going to do much. If you bend too hard, the tree snaps. Either of these results doesn't help much. It takes quite a bit of practice to get it down correctly, and every once and awhile you will have a snapped limb.