A binary search tree is a special binary tree, which is either empty or it should satisfy the following characteristics:

Every node has a value and no two nodes should have the same value i.e) the values in the binary search tree are distinct.
The values in any left sub-tree is less than the value of its parent node.
The values in any right sub-tree is greater than the value of its parent node.
The left and right sub-trees of each node are again binary search trees.   _{Your Comment}