Need help for three BinaryTree class

public class BinaryTree {

//Implements a Binary Tree of Strings

private class Node {

private Node left;

private String data;

private Node right;

private Node parent; // reference to the parent node

// the parent is null for the root node

private Node(Node L, String d, Node r, Node p) {

left = L;

data = d;

right = r;

parent = p;

}

}

private Node root;

public BinaryTree() {

// create an empty tree

root = null;

}

public BinaryTree(String d) {

// create a tree with a single node

root = new Node(null, d, null, root);

}

public BinaryTree(BinaryTree b1, String d, BinaryTree b2) {

// merge the trees b1 AND b2 with a common root with data d

}