private T removeHelper(BSTNode<T> parent, T data) {
        T output = null;
        if (parent == null) {
            throw new NoSuchElementException("element not found");
        }
        if (parent == root && root.getData().compareTo(data) == 0) {

            if (parent.getRight() == null) {
                parent = parent.getLeft();
            } else if (parent.getLeft() == null) {
                parent = parent.getRight();
            } else {
                parent.setData(successor(root));
            }
        } else if (data.compareTo(parent.getData()) < 0) {
            if (parent.getLeft() == null) {
                return null;
            } else if (parent.getLeft().getData().compareTo(data) == 0) {
                output = parent.getLeft().getData();
                if (parent.getLeft().getRight() == null) {
                    parent.setLeft(parent.getLeft().getLeft());
                } else if (parent.getLeft().getLeft() == null) {
                    parent.setLeft(parent.getLeft().getRight());
                } else {
                    parent.getLeft().setData(successor(parent.getLeft()));
                }

            } else {
                output = removeHelper(parent.getLeft(), data);
            }
        } else {
            if (parent.getRight() == null) {
                return null;
            } else if (parent.getRight().getData().compareTo(data) == 0) {
                output = parent.getRight().getData();
                if (parent.getRight().getLeft() == null) {
                    parent.setRight(parent.getRight().getRight());
                } else if (parent.getRight().getRight() == null) {
                    parent.setRight(parent.getRight().getLeft());
                } else {
                    parent.getRight().setData(successor(parent.getRight()));
                }
            } else {
                output = removeHelper(parent.getRight(), data);
            }
        }
        return output;
    }