What Is a Tree in Data Structure and Graph?


Larry Thompson

A tree is a fundamental data structure in computer science and graph theory. It is a hierarchical structure that resembles a real-life tree, with a root node at the top and child nodes branching out from it. Trees are widely used to represent hierarchical relationships, such as file systems, organization charts, and family trees.

Tree Terminology

Before we dive deeper into trees, let’s familiarize ourselves with some common terminology:

  • Node: Each element in a tree is called a node. It contains data and may have zero or more child nodes.
  • Root: The topmost node of a tree is called the root.

    It has no parent.

  • Parent: A node that has one or more child nodes is called a parent. The root node has no parent.
  • Child: Nodes directly connected to a particular node are its children.
  • Leaf: A leaf node is a node that has no children.
  • Sibling: Nodes that share the same parent are called siblings.
  • Depth: The depth of a node represents the number of edges from the root to that particular node.
  • Height: The height of a tree is the maximum depth of any node in the tree.

The Structure of Trees

Trees consist of interconnected nodes with specific relationships. Each child can only have one parent, but each parent can have multiple children. This creates a hierarchical structure where information flows from the root to its descendants.

Binary Trees

A binary tree is a type of tree where each parent can have at most two children. The left child is referred to as the left subtree, and the right child is called the right subtree. Binary trees are commonly used in various algorithms and data structures.

Binary Search Trees

A binary search tree (BST) is a type of binary tree that follows a specific ordering property. In a BST, all nodes in the left subtree of a node must have values less than the node’s value, and all nodes in the right subtree must have values greater than the node’s value. This property makes searching, inserting, and deleting elements in BSTs efficient.

Applications of Trees

Trees have numerous applications in computer science:

  • File Systems: File systems often utilize trees to represent directories and files, with directories acting as parent nodes and files as leaf nodes.
  • Database Indexing: B-trees are commonly used in database systems to efficiently store and retrieve data.
  • Game Trees: Game trees are used in artificial intelligence to represent possible moves and outcomes in games like chess or tic-tac-toe.
  • Hierarchical Data Representation: Trees are ideal for representing hierarchical relationships such as organization charts or family trees.


Trees are versatile data structures that allow us to organize information hierarchically. Understanding their structure and properties enables us to solve complex problems efficiently. Whether you’re working with file systems, databases, or game algorithms, having a solid understanding of trees will undoubtedly be beneficial!

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