title: How do I add a submenu to an existing menu in Magento?
body: <p>My existing code creates a menu that looks like this.</p>
  
  <p><img src="https://i.stack.imgur.com/VgN3w.png" alt="custom magento menu"></p>
  
  <p>But I want a menu that is a sub-menu of the Catalog menu.</p>
  
  <p>Here is my existing code in <code>adminhtml.xml</code></p>
  
  <pre><code>&lt;?xml version="1.0" ?&gt;
  &lt;config&gt;
      &lt;menu&gt;
          &lt;mycustom_menu translate="title" module="brands"&gt;
              &lt;title&gt;My Custom Menu Item&lt;/title&gt;
              &lt;sort_order&gt;300&lt;/sort_order&gt;
              &lt;children&gt;
                  &lt;!-- child items go here --&gt;
                  &lt;subitem translate="title" module="brands"&gt;
                      &lt;title&gt;Manage Brands&lt;/title&gt;
                      &lt;sort_order&gt;10&lt;/sort_order&gt;
                      &lt;action&gt;adminhtml/mycustom_controller/&lt;/action&gt;
                  &lt;/subitem&gt;
              &lt;/children&gt;
          &lt;/mycustom_menu&gt;
      &lt;/menu&gt;
      &lt;acl&gt;
          &lt;resources&gt;
              &lt;admin&gt;
                  &lt;children&gt;
                      &lt;mycustom_menu translate="title" module="brands"&gt;
                          &lt;title&gt;My Custom Menu Item&lt;/title&gt;
                          &lt;sort_order&gt;300&lt;/sort_order&gt;
                          &lt;children&gt;
                              &lt;subitem translate="title" module="brands"&gt;
                                  &lt;title&gt;Subitem&lt;/title&gt;
                                  &lt;sort_order&gt;10&lt;/sort_order&gt;
                              &lt;/subitem&gt;
                          &lt;/children&gt;
                      &lt;/mycustom_menu&gt;
                  &lt;/children&gt;
              &lt;/admin&gt;
          &lt;/resources&gt;
      &lt;/acl&gt;
  &lt;/config&gt;
  </code></pre>