# Trees Introduction
- Tree data structure is a collection of Nodes (Data) which are organized in hierarchical structure
Parent Node - the node which has branch from it to any other node is called a parent node.
Child Node - the node which is descendant of any node is called a child Node & all the nodes except A are child nodes.
Root Node - The first node of the tree is called the Root Node. It is the origin of tree data structure & in any tree, there is only one root node.
Leaf Node - the node which does not have a child is called as Leaf Node & the leaf nodes are also called as External Nodes.
Internal Node - the node which has at least one child is called an Internal Node.
- Degree - the total number of children of a node is called as Degree of that Node &The highest degree of a node among all the nodes is called as Degree of Tree. i.e. 3
- Level - In a tree each step from top to bottom is called as a Level & We start the levels from root node taking it as Level 0.