public static boolean equal(BinaryTreeNode t1, BinaryTreeNode t2) {
		
		if (t1 == null && t2 == null) {
			return true;
		}
		
		if ((t1 == null && t2 != null) || (t1 != null && t2 == null)) {
			return false;
		}
		
		if (t1.data != t2.data){
			return false;
		}
		
		boolean leftAreEqual = equal(t1.leftChild, t2.leftChild);
		boolean rightAreEqual = equal(t1.rightChild, t2.rightChild);
		
		return leftAreEqual && rightAreEqual;
		
	}