In the sequence of tiles shown below, the missing tile indicated by the question mark should be $$\boxed{\begin{matrix} \ \ \ \ \ \ \bullet \\ \\ \bullet \ \ \ \ \ \end{matrix}} \quad \boxed{\begin{matrix} \ \ \ \ \ \ \bullet \\ \ \ \ \bullet \\ \bullet \ \ \ \ \ \end{matrix}} \quad \boxed{\begin{matrix} \ \ \ \ \ \ \ \ \\ \ \ \ ? \ \ \ \\ \ \ \ \ \ \ \ \end{matrix}} \quad \boxed{\begin{matrix} \bullet \ \bullet \ \bullet \\ \ \ \ \bullet \\ \bullet \ \bullet \ \bullet \end{matrix}} \quad \boxed{\begin{matrix} \bullet \ \bullet \ \bullet \ \bullet \\ \ \bullet \ \bullet \ \bullet \\ \bullet \ \bullet \ \bullet \ \bullet \end{matrix}}$$