What Is Binary Expression Tree in Data Structure?


Heather Bennett

A binary expression tree is a type of data structure used to represent mathematical expressions. It is a binary tree where each internal node represents an operator, and each leaf node represents an operand.

Structure of a Binary Expression Tree

In a binary expression tree, the operands are stored in the leaf nodes, while the operators are stored in the internal nodes. The tree has the following properties:

  • Leaf Nodes: Leaf nodes contain operands such as numbers or variables.
  • Internal Nodes: Internal nodes contain operators such as addition (+), subtraction (-), multiplication (*), and division (/).
  • Root Node: The topmost node of the tree is called the root node. It represents the entire expression.

To visualize a binary expression tree, consider the following arithmetic expression:

(5 + 3) * 2

This expression can be represented using a binary expression tree as shown below:

       /   \
      +     2
     / \
    5   3

Benefits of Binary Expression Trees

Binary expression trees offer several advantages:

  • Evaluation: Binary expression trees provide an efficient way to evaluate arithmetic expressions. By traversing the tree in a specific manner, we can easily compute the result of an expression.
  • Parsing: Binary expression trees can be used to parse and interpret mathematical expressions. They help in understanding operator precedence and associativity.
  • Simplicity: Once constructed, binary expression trees simplify complex expressions by breaking them down into smaller sub-expressions.

Evaluating a Binary Expression Tree

To evaluate a binary expression tree, we perform a postorder traversal of the tree. Here’s how the evaluation process works:

  1. If the current node is an operand (leaf node), return its value.
  2. If the current node is an operator, recursively evaluate its left and right subtrees.
  3. Apply the operator to the results obtained from step 2 and return the final result.

Using the previous example, let’s evaluate the expression:

We start from the bottom of the tree:

  1. The left subtree (5 + 3) evaluates to 8.
  2. The right subtree (2) evaluates to 2.
  3. Multiplying the results from step 1 and step 2 gives us the final result: 8 * 2 = 16.


A binary expression tree is a valuable data structure for representing and evaluating mathematical expressions. It helps in simplifying complex expressions and provides a systematic way to parse and interpret arithmetic operations. By understanding its construction and evaluation process, you can apply binary expression trees in various applications that involve mathematical computations.

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