public:
    // Is Empty ?
    bool isEmpty() const {
        return root==NULL;
    }
    // Clear
    void clear() {
        if(isEmpty())
            return;
        root = clearTreeRecursively();
    }
    // = Operator Overloading
    const BST & operator=(const BST &BT) {
        root = clearTreeRecursively();
        root = copyAs(BT.root);
    }

    // == Operator Overloading
    const BST & operator(const BST &BT) {
        return isSame(root, BT.root);
    }
    // Size
    int size() const {
        return sizeHelper(root);
    }
// Size Helper
private:
    static int sizeHelper(const Node<T> *node) {
        if(!node)
            return 0;
        return sizeHelper(node->left) + sizeHelper(node->right) + 1;
    }