Cage tree

A Cage tree is a tree which grows in a ball shape. The trunk grows vertically straight up, and branches grow off the top of the trunk, bend around, and connect back to the tree at the bottom.

Cage trees are commonly used by farmers to store animals in, or by slavers to store slaves in - when chopped down at the base of the trunk, the rest of the tree hardens, and becomes incredibly tough (some claim "impossible") to break. The toughness of the tree depends on the conditions in which it is grown, and as such, Cage tree farming can be quite lucrative if the right combination of nutrients is found.