The way in which you dig up a tree or any other large plant can change a lot depending upon two factors; how big their root system is, and whether or not you intend to replant the plant elsewhere. If you’re digging up the tree with the intention of getting rid of it, you can obviously be less careful about how you treat the roots, but if you want to move it to another spot being careful and trying to avoid causing much damage is the aim of the game.
Digging up as much of the roots as possible while in one piece is clearly the best way of ensuring that the tree survives the transportation, but this isn’t always achievable, and so a compromise is usually used. This is where you up the tree a long with the root ball; the part of the root system closely connected to the base of the tree trunk, before the roots start to branch out. This is where the the largest portion of the tree’s root mass is stored, and preserving this is key to the tree’s survival.