public class TreeNode<E> {
    public E data;		  // data stored at this TreeNode<E>
    public TreeNode<E> left;  // reference to left subtree
    public TreeNode<E> right; // reference to right subtree
		
    // post: constructs a leaf node with given data
    public TreeNode(E data) {
        this(data, null, null);
    }
				
    // post: constructs a TreeNode<E> with the given data and links
    public TreeNode(E data, TreeNode<E> left, TreeNode<E> right) {
        this.data = data;
        this.left = left;
        this.right = right;
    }
}