# Binary trees

Generally speaking, each node in a basic tree can contain any number of children. However, in the case of **binary trees**, **a node cannot contain more than two children**. It means that **it can contain zero,*** ***one, or two child nodes**. Such a requirement has an important impact on the shape of a binary tree, as shown in the following two diagrams presenting binary trees:

Figure 7.4 – Illustration of binary trees

As already mentioned, a node in a binary tree can contain at most two children. For this reason, they are referred to as the **left child** and the **right child**. In the case of the binary tree shown on the left-hand side of the preceding diagram, node **21** has two children, namely **68** as the left child and **12** as the right child, while node **100** has only a left child.

## Traversal

Have you thought about how you can iterate through all the nodes in a tree? How can you specify an order of nodes during **traversal** of a tree? There are three common...