A stunt tree is a series of stunts that have prerequisites. In other words, once you have stunt A, you are allowed to get stunts B, C, and D as well. And if you get stunt D, whether or not you get B or C, you can then also choose stunts E and F. But you might want stunt B because it lets you get stunt G. So yeah, with the different branches it starts to look like a tree.
But today we are not really going to focus so much on what stunt trees are. Rather, we would like to delve a little more into the WHY. After all, in the Fate Core system any player can make any stunt they wish (under the basic rules), so what’s the point of making some stunts harder to get than others?