title: Change sub-menu wrap in Wordpress
body: <p>In Wordpress, how can I add a button or div into all sub-menu li's using wp_nav_menu?</p>
  
  <p>This is my current code:</p>
  
  <pre><code>&lt;?php wp_nav_menu(array(
    'theme_location' =&gt; 'main_menu', 
    'items_wrap'=&gt;'%3$s', 
    'container' =&gt; false
  )); ?&gt;
  </code></pre>
  
  <p>This is my desired output:</p>
  
  <pre><code>&lt;li class="submenu"&gt;
    &lt;a&gt;Link 1&lt;/a&gt;
    &lt;ul&gt;
      &lt;li&gt;&lt;a&gt;Link 2&lt;/a&gt;&lt;/li&gt;
    &lt;/ul&gt;
    &lt;button type="button"&gt;Click Me!&lt;/button&gt; 
  &lt;/li&gt;
  </code></pre>