A tree view or an outline view is a graphical control element that presents a hierarchical view of information. Each item (often called a branch or a node) can have a number of subitems. This is often visualized by indentation in a list.
An item can be expanded to reveal subitems, if any exist, and collapsed to hide subitems.
Extended tree view is the central component of outliner applications, where each node consists of editable text.