How Tree Is Used in Data Structure in Python?


Angela Bailey

Tree is a widely used data structure in Python, which serves as an efficient way to store and organize hierarchical data. It has various applications in computer science and is commonly used in algorithms such as search, sort, and traversal. In this article, we will explore the concept of trees and how they can be implemented in Python.

What is a Tree?

A tree is a hierarchical data structure that consists of nodes connected by edges. It is composed of a root node, which acts as the starting point, and zero or more child nodes that branch out from the root. Each node can have any number of child nodes, but can only have one parent node.

Trees are similar to real-life trees, where the root represents the trunk and the child nodes represent branches. The topmost node is called the root node, while the bottommost nodes with no children are called leaf nodes.

Tree Terminology

Before diving into tree implementation in Python, let’s familiarize ourselves with some important tree terminologies:

  • Node: A single element in a tree that contains data and references to its child nodes.
  • Root: The topmost node in a tree that does not have any parent node.
  • Leaf: A node that does not have any child nodes.
  • Parent: A node that has one or more child nodes.
  • Child: A node that has a parent node.
  • Sibling: Nodes with the same parent are called siblings.

Implementing Trees in Python

In Python, we can implement trees using classes and objects. Each node in the tree can be represented by a class, which contains the necessary data and references to its child nodes. Let’s take a look at a simple implementation of a tree in Python:

class TreeNode:
    def __init__(self, data): = data
        self.children = []

    def add_child(self, child):

In the above code snippet, we define a TreeNode class with an __init__ method that initializes the node with its data and an empty list to store its children. We also define an add_child method to add children to the node.

To create a tree using this implementation, we start by creating an instance of the root node:

root = TreeNode("A")

We can then add child nodes to the root using the add_child method:


This creates a tree structure where “A” is the root node and “B”, “C”, and “D” are its child nodes.

Tree Traversal

Tree traversal refers to visiting each node in a tree exactly once. There are three common methods for traversing trees: depth-first traversal, breadth-first traversal, and level-order traversal.

Depth-First Traversal

In depth-first traversal, we start at the root node and visit all its children before moving on to their children. This process continues until all nodes have been visited. There are three types of depth-first traversal:

  • Pre-order traversal: Visit the root node first, then recursively visit its children from left to right.
  • In-order traversal: Recursively visit the left child, then the root node, and finally the right child.
  • Post-order traversal: Recursively visit the children from left to right, and finally visit the root node.

Breadth-First Traversal

In breadth-first traversal, we visit all nodes at the same level before moving on to nodes at the next level.

Level-Order Traversal

In level-order traversal, we visit nodes level by level. We start with the root node and move on to its children, then their children, and so on.


Trees are a powerful data structure that allows us to efficiently store and organize hierarchical data. In Python, trees can be implemented using classes and objects.

Understanding tree terminology and various tree traversal methods is crucial for effectively working with trees in Python. With this knowledge, you can leverage trees to solve complex problems in computer science and programming.

I hope this article has provided you with a thorough understanding of how trees are used in data structures in Python!

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