Binary Trees are one of the most important topics in Data Structures. ECET exam frequently asks questions on tree basics, insertion, and tree traversals. If you understand how nodes are inserted and how traversal order works, you can score 2–3 marks easily.

📘 Concept Notes – Binary Tree

🌳 What is a Binary Tree?

A Binary Tree is a tree data structure where:

• Every node can have at most two children → Left child & Right child.
• Each node contains data, left pointer, right pointer.

⚙️ Binary Tree Insertion (General Binary Tree)

Insertion in a simple binary tree (not BST) is usually done level-by-level using a queue.

Steps (Level-order insertion):

1. Start from the root.
2. Check if the left child is empty → insert there.
3. Else check right child → insert there.
4. If both filled → move to next level with queue.

Example

Insert: 10, 20, 30, 40, 50

Tree becomes:

        10
       /  \
     20    30
    / \
  40   50

        10
       /  \
     20    30
    / \
  40   50

Insertion in Binary Search Tree (BST)

(If ECET asks BST questions)

Rules:

• If new value < node → go to left
• If new value > node → go to right

Example: Insert 50, 30, 70, 20, 40

        50
       /  \
     30    70
    / \
  20   40

        50
       /  \
     30    70
    / \
  20   40

Binary Tree Traversals

Traversal means visiting all nodes in a specific order. There are three standard depth-first traversals.

1️⃣ Inorder Traversal (Left → Root → Right)

Order formula:

Example Tree:

        10
       /  \
     20    30

        10
       /  \
     20    30

Inorder = 20, 10, 30

2️⃣ Preorder Traversal (Root → Left → Right)

Order formula:

Output for example tree:
Preorder = 10, 20, 30

3️⃣ Postorder Traversal (Left → Right → Root)

Order formula:

Output:
Postorder = 20, 30, 10

📦 Example for All Traversals

Consider this tree:

         1
       /   \
      2     3
    /  \   / \
   4    5 6   7

         1
       /   \
      2     3
    /  \   / \
   4    5 6   7

✔ Inorder

4, 2, 5, 1, 6, 3, 7

✔ Preorder

1, 2, 4, 5, 3, 6, 7

✔ Postorder

4, 5, 2, 6, 7, 3, 1

🔢 🔟 10 Most Expected MCQs – ECET 2026

Q1. A binary tree node has at most:
A) 1 child
B) 2 children
C) 3 children
D) Unlimited children

Q2. Inorder traversal order is:
A) Root, Left, Right
B) Left, Right, Root
C) Left, Root, Right
D) Root, Right, Left

Q3. Preorder traversal starts with:
A) Left
B) Right
C) Root
D) Leaf

Q4. Insertion in a simple binary tree is done using:
A) DFS
B) BFS (level order)
C) Inorder
D) Stack

Q5. For BST, if new value < node value, it goes to:
A) Right
B) Left
C) Root
D) Deleted

Q6. Postorder ends with:
A) Left
B) Right
C) Root
D) Any node

Q7. Level-order traversal uses:
A) Queue
B) Stack
C) Tree
D) Graph

Q8. For this tree, what is preorder?

    5
   / \
  3   7

    5
   / \
  3   7

A) 3, 5, 7
B) 5, 3, 7
C) 3, 7, 5
D) 7, 5, 3

Q9. Maximum number of nodes at level in a binary tree is:
A)
B)
C)
D)

Q10. Height of a tree with 1 node is:
A) 0
B) 1
C) 2
D) Undefined

✅ Answer Key

🧠 Explanations (Short & Clear)

• Q1: Binary tree → max 2 children.
• Q2: Inorder always L → R → R.
• Q3: Preorder always starts with root.
• Q4: Binary tree insertion uses BFS → queue.
• Q5: For BST, smaller values go left.
• Q6: Postorder ends with root.
• Q7: Level-order = queue.
• Q8: Preorder = Root, Left, Right → 5, 3, 7.
• Q9: At level k → nodes possible.
• Q10: Single node tree height = 0.

🎯 Why Practice Matters

Binary Trees appear constantly in DS exam papers.
If you understand:

• how insertion works
• and how traversals work

…you can answer any ECET tree question confidently.

📲 Join Our ECET WhatsApp Community

👉 Join WhatsApp Group:
https://chat.whatsapp.com/GniYuv3CYVDKjPWEN086X9