What Is a Tree Diagram? A tree diagram is a tool in the fields of general mathematics, probability, and statistics that helps calculate the number of possible outcomes of an event or problem, and ...

Tree diagrams are a way of showing combinations of two or more events. Each branch is labelled at the end with its outcome and the probability is written alongside the line.

Data viz isn’t just a modern-day craze. Designer Manuel Lima, author of The Book of Trees, discusses the origins of the tree diagram.