Folks who buy a young tree that has grown in a container a bit too long want to know what to do about the roots--score the rootball vertically? cut off the circling roots at the bottom of the root ball, fluff up the rootball, bash the rootball until it loosens?
I start with what a tree wants to do, namely, make four or five major roots that spread out. Indeed, trees in container do so, but the would-be major roots run into the sides of the container and have nowhere to go. Gravity commands them to descend and they do until they hit the bottom of the container, where they keep growing by growing sideways, eventually in a circle.
I completely untangle the rootball and spread it out so the major root and all their branches are heading outward, equally spaced.
The photos here show the process, with hints along the way.