class TreeNode {
    public int val;
    public TreeNode left;
    public TreeNode right;

    public TreeNode(int x) { 
        val = x; 
        left = null; 
        right = null; 
    }
}

public class BinarySearchTree {

    private TreeNode root;

    // Adds a new node with key to the binary search tree.
    public void insert(int key){
        
        // Base case: if no tree, then create one
        if (root == null) {
            this.root = new TreeNode(key);            
        }
        else { 
           
            // find and return root where our key should be inserted. This is called the "search" method.
            Node current = search(this.root, key);
            int leftVal = (int)(current.left.val);

            if ((leftVal == 0) && !key.equals(leftVal)) {
                this.root.left = new TreeNode(key);                
            }
            else{
            
                // If not inserted yet or a duplicate is found
                Node current2 = search(current.right, key);
                int rightVal = (int)(current2.right.val);

                if ((rightVal == 0) && !key.equals(rightVal)) {
                    this.root.left = new TreeNode(key);                
                }
            }            
        }

    }
}