Insert Node in a Binary Search Tree

Problem

Given a binary search tree and a new tree node, insert the node into the tree. You should keep the tree still be a valid binary search tree.

Example

Given binary search tree as follow, after Insert node 6, the tree should be:

      2             2
     / \           / \
    1   4   -->   1   4
       /             / \
      3             3   6

Challenge

Can you do it without recursion?

Code - Java

/**
 * Definition of TreeNode:
 * public class TreeNode {
 *   public int val;
 *   public TreeNode left, right;
 *   public TreeNode(int val) {
 *     this.val = val;
 *     this.left = this.right = null;
 *   }
 * }
 */
public class Solution {
    /**
     * @param root: The root of the binary search tree.
     * @param node: insert this node into the binary search tree
     * @return: The root of the new binary search tree.
     */
    public TreeNode insertNode(TreeNode root, TreeNode node) {
        if (root == null) {
            return node;
        }
        if (node.val > root.val) {
            if (root.right == null) {
                root.right = node;
            } else {
                insertNode(root.right, node);
            }
        } else if (node.val < root.val) {
            if (root.left == null) {
                root.left = node;
            } else {
                insertNode(root.left, node);
            }
        }
        return root;
    }
}