It is widely used in probability theory – as a tool to estimate and visualize probabilities, where the possible outcome of a certain sequence of events is depicted at the end of each branch of the tree diagram.

Its name came from the shape this diagram takes: it starts off one item (a trunk) that branches out into two or more following items, branches out more and more, and so on (multiple branches). The shape makes it easy to see at a glance what needs to be done (and in what order) to get the project done, as it breaks down broad abstract or general categories into doable tasks and subtasks.

The example of usage of a tree diagram:

• When there is a need to address specific tasks needed to solve a general known problem  

• When there is a need to estimate a possible outcome and analyzed a developed process in details

• When there is a need to evaluate implementation issues for several potential outcomes