public int range(int min, int max) {
        //throw exception if min < max
        if(min > max){
            throw new IllegalArgumentException("Range was not valid. Please insert min < max");
        }
        if(root != null){
            rangeSearch(root, min, max);
        }
        else {
            throw new EmptyException("Tree is empty");
        }
        return rangeSearch(root, min, max);

    }

    private int rangeSearch(BTNode<Integer> root, int min, int max){
        //check if tree is empty
        if(root == null){
            return 0;
        }
        if (root.data == max && root.data == min){
            return 1;
        }
        if (root.data <= max && root.data >= min){
            return 1 + rangeSearch(root.left, min, max) + rangeSearch(root.right, min, max);
        }
        else if(root.data < min){
            return rangeSearch(root.right, min, max);
        }
        else return rangeSearch(root.left, min, max);
    }