def insert(self, value, index) -> None:
        curr = self._first
        cnt = 0
        if curr is None and index == 0:
            # when index is 0 and self._first is None
            self._first = Node(value)
            return None
        else:
            while curr is not None:
                # when reached at index
                if cnt == index:
                    new_node = Node(curr.value)
                    new_node._next = curr._next
                    curr._value = value
                    curr._next = new_node
                cnt += 1
                curr = curr._next
                return None
            raise IndexError