title: Custom BarButtonItem Item: Add red dot on top right corner, Swift 4 IOS
body: <p>I want to add/set unread flag as red dot top right corner on <code>UIbarButtonItem</code>, See attached image for this</p>
  
  <p><a href="https://i.stack.imgur.com/5lDNm.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/5lDNm.png" alt="enter image description here"></a></p>
  
  <p>What should i do to add/set red dot on Bar Button item?
  Once user tap on item then i want to remove red dot.</p>