Like real trees, tree data structures exhibit branching. This carries a number of implications.

First, one must consider the degree of a tree. This refers to the maximum number of children that a node can have. The most common form of tree in computer science is a binary tree, in which each node can have up to 2 children. There are however, ternary trees, with up to 3 children, quaternary trees with up to four children, and so forth.

The next element to consider is the overall size of the tree. There are a number of ways to quantify tree size. One is the longest path from the root node to a leaf node. This is called the depth. If you imagine a tree as having layers, the depth is the number of layers.

When describing a tree, it is often convenient to be able to describe its form in detail. There are several terms which describe the form of trees. A balanced tree is one where all of the leaves of the tree are within one layer of one of each other. For example:

is a balanced tree, whereas the following is not: