```html
<!DOCTYPE html>
<html>
<body>

<ul>
  <li><a href="#home">Home</a></li>
  <li><a href="#news">News</a></li>
  <li><a href="#contact">Contact</a></li>
  <li><a href="#about">About</a>
  <ul>
  <li>profile</li>
  <li>details</li>
  </ul></li>
</ul>

</body>
</html>
```

I have this simple `li` in my header as menus.I am just trying to add sub list like when I click on `about` sub list should be displayed. How can I do it?