### Wide and deep trees

There are two ways to describe the shape of a tree. Trees can be *wide*, meaning that each node has many children. And trees can be *deep*, meaning that there are many parent-child connections with few siblings per node. Trees can be both *wide* and *deep* at the same time.

### Binary search tree

In a *binary search tree*, parent nodes can have a maximum of two children. These children are called the “left child” and the “right child”. A binary search tree requires that the values stored by the left child are **less** than the value of the parent, and the values stored by the right child are **greater** than that of the parent.

### Nodes as parents

Trees in computer science are often talked about similarly to family trees. A tree node that references one or more other nodes is called a “parent”.

A tree node can be a “parent” and a “child” simultaneously, because they are not exclusive. For instance, a node ‘b’ can be the child of node ‘a’, while being the parent to nodes ‘d’ and ‘e’. However, a child can only have one parent, while a parent can have multiple children.

### Trees are composed of nodes

Trees are a data structure composed of nodes used for storing hierarchical data.

Each tree node typically stores a value and references to its child nodes.

### Tree nodes children

A tree node contains a value, and can also include references to one or more additional tree nodes which are known as “children”.

### Node root

In a tree data structure, the node that is not the child of any other node is called the *root* of the tree. A tree can only have one root.