title: Material UI: drawer with expandable side menu
body: <p>Using Material UI, how can I construct a Drawer with expandable menu items like the one on the <a href="https://v1-1-0.material-ui.com/demos/app-bar/" rel="noreferrer">material-ui.com</a> site?</p>
  
  <p>So I want something like this:
  <a href="https://i.stack.imgur.com/8VqMi.png" rel="noreferrer"><img src="https://i.stack.imgur.com/8VqMi.png" alt="enter image description here"></a></p>
  
  <p>Each menu item (in bold) can expand to reveal sub-menu items.</p>
  
  <p>How can this be achieved with Material UI?</p>