title: Searching for a vertical Bootstrap navbar with folding sub-items on hover
body: <p>I'm writing a Bootstrap web site and now I'm facing a problem with the navbars.</p>
  
  <p>In a nutshell, I'd like to show a vertical navigation bar with several image buttons; hovering on some of them should open an horizontal menu made up of other image buttons.
  The image below sums up the idea</p>
  
  <p><img src="https://i.stack.imgur.com/ZCLiy.png" alt="enter image description here"></p>
  
  <p>Do you know whether there is any Bootstrap class which can help me?</p>