text: /**
   *           10
   *      6        15
   *  3      8         20
   *
   * post order - [3,8,6,20,15,10] 
   * 
   * Psuedocode (Recursive)
   * 1. Create a variable to store the values of nodes visited.
   * 2. Store the root of the BST in a variable called current.
   * 3. Write a helper function which accepts a node
   *      - If the node has a left property, call the helper function with the left property of the node.
   *      - If the node has a right property, call the helper function with the right property of the node.
   *  	- Push the value of the node to the variable that stores the values.
   * 4. Invoke the helper function with the current value.
   * 5. Return the array of values.
   */
  
  function DFSPostOrder() {
   var data = [];
   var current = this.root;
  
   function traverse(node) {
       if(node.left) traverse(node.left);
       if(node.right) traverse(node.right);
       data.push(node.value);
   }
   traverse(current);
   return data;
  }