How to make this pattern using Walker_Nav_Menu?

<ul class="nav navbar-nav">
      <li><a href="portfolio.html">Portfolio</a></li>
      <li class="dropdown">
          <a href="#" class="dropdown-toggle" data-toggle="dropdown">Pages <i class="fa fa-angle-down"></i></a>
          <ul class="dropdown-menu">
              <li><a href="blog-item.html">Blog Single</a></li>
          </ul>
      </li>
</ul>