A **Tree** is a hierarchical data structure that is different from linear data structures like arrays, linked lists, stacks, and queues. A **subtree** is a part of the tree below any chosen node that can be considered as a separate tree with that node as a root node. Subtree is very much similar to the sub-directory which lies inside of a root directory as in our computer systems.

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**Binary Tree**is a type of tree in which each node cannot have more than 2 children nodes. These types of trees are very important and are used extensively. **The root node**of a Binary Tree is the top-most node from where the tree hierarchy begins.**Leaf nodes**are those nodes that lie at the terminal part of the tree indicating the last or bottom-most part of the tree.**Children**of a node are the nodes to which the pointers from the node directly point. These nodes lie directly below or in the next hierarchical level of the chosen node.**The ancestors**of a given node are all the nodes that come before the node while traversing from the root node to the given node.

There are different types of Binary Trees:

**Full Binary Tree –**It is a type of tree in which each node has either 0 or 2 children.

2. **Complete Binary Tree – **It is a type of tree where all the levels of the tree are filled with nodes except the last level. The last level must have each node as left as possible.

3. **Perfect Binary Tree – **It is a type of tree in which all the leaf nodes should be on the same level.

4. **Balanced Binary Tree – **In a balanced binary tree, the height of the tree should be at max log(N), where N is the number of nodes. The tree should not be skewed.

5. **Degenerate Tree – **A degenerate tree is a skewed tree that is similar to a linked list where each node is connected to the left of the previous node and the tree goes leftwards only.

Say, for N = 4, the degenerate tree would look like this:

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