title: Add item to existing menu in Google Apps Script
body: <p>How do I add an item to an existing menu (in Google Docs) in Google Apps Script?</p>
  
  <p>I can create a <em>new</em> menu and add an item to that:</p>
  
  <pre><code>DocumentApp.getUi().createMenu('MyMenu')
    .addItem('Insert My Thing', 'myFunction')
    .addToUi();
  </code></pre>
  
  <p>But it seems a bit ridiculous to add a whole menu for a single item that should really go under the existing "Insert" menu.</p>