Added - What is BST

README.md

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 # BinarySearchTree
 A binary search tree which includes insertion, deletion, inorder printing of the string.
+##Added by Tejas Amle
+
+A Binary Search Tree (BST) is a tree in which all the nodes follow the below-mentioned properties −
+
+The left sub-tree of a node has a key less than or equal to its parent node's key.
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+The right sub-tree of a node has a key greater than to its parent node's key.
+
+Thus, BST divides all its sub-trees into two segments; the left sub-tree and the right sub-tree and can be defined as −
+
+left_subtree (keys)  ≤  node (key)  ≤  right_subtree (keys)
+Representation
+BST is a collection of nodes arranged in a way where they maintain BST properties. Each node has a key and an associated value. While searching, the desired key is compared to the keys in BST and if found, the associated value is retrieved.
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+Following is a pictorial representation of BST −
+
+Binary Search Tree
+We observe that the root node key (27) has all less-valued keys on the left sub-tree and the higher valued keys on the right sub-tree.
+
+Basic Operations
+Following are the basic operations of a tree −
+
+Search − Searches an element in a tree.
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+Insert − Inserts an element in a tree.
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+Pre-order Traversal − Traverses a tree in a pre-order manner.
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+In-order Traversal − Traverses a tree in an in-order manner.
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+Post-order Traversal − Traverses a tree in a post-order manner.