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Tree Data Structure Terminologies – Set 1

July 1, 2018
Posted by Abhi Andhariya

In this article, we will discuss one of the important non-linear data structure in computer science, Tree. Many real-life problems can be represented and solved using Tree data structure. 

In this article, we will understand basic tree terminologies like Nodes, Edges, Root, Parent, Children, Leaves and Siblings. In next article on tree terminologies, we will see  terms like Degree of Tree, Path, Level, Depth, Height of tree and sub tree. 

How tree is different than other data structures? 

Array, Stack, Queue and Linked List are Linear data structures where as Tree is non- linear data structure like Graph.

But tree is special form of graph having only one path between any two nodes. Tree is a special case of graph having no loops, no circuits and no self-loops.

A tree is an ideal data structure for representing hierarchical data. Lets start with some of the basic terminologies being used for ​Tree.

Tree Data Structure

Tree Terminologies / Tree Vocabulary

Nodes and Edges/Branches

Tree is a type of data structure in which each element is attached to one or more elements directly beneath it. These elements are called Nodes and the connections between them are called branches. If we have total N nodes in tree, then we can have maximum N-1 edges between them. e.g in below Tree, there are 10 nodes and 9 edges.

Nodes vs Edges in Tree data structure

Root Node

Top most node of the Tree is called root of the Tree. We can say that root node is the origin of Tree data structure. Every Tree must have exact one root node (Not less not more). In above tree, is a root Node.


In tree data structure, Node which has at least one child node is known as Parent Node.  Parent Nodes (except root Node) are also known as Internal Nodes or Non-Terminal nodes. If there are more than one nodes in tree, then Root Node is also a Parent Node  or Internal Node.


In a tree, a Parent can have any number of child nodes. All nodes except Root Node are children.

Leaf Nodes

In a tree, Node which does not have any child is called Leaf Node. Leaf nodes are also known as External Nodes or Terminal Nodes. In other words, all the nodes except leaf nodes are parent nodes.

Parents and Children Tree Data Structure

Trees are often called Inverted Tree  because  they are normally drawn  with root  at the top and leaves at bottom.


Nodes which belong to same parent are called siblings.


siblings in Tree data structure

That's all for this topic. If you guys have any suggestions or queries, feel free to drop a comment. We would be happy to add that in our post. You can also contribute your articles by creating contributor account here.

Happy Learning 🙂

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Surviving Java Developer, Passionate Blogger, Table Tennis Lover, Bookworm, Occasional illustrator and a big fan of Joey Tribbiani, The Walking Dead and Game of Thrones...!!

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