title: How to add Variations tab in custom product type in Woocommerce?
body: <ul>
  <li>I've installed a plugin for "Gift Cards", which is basically adding a
  product type "Gift card".  
  
  <ul>
  <li>I need to enhance its functionality.</li>
  <li>There are other tabs available for this but the tab "Variations" is
  not.</li>
  <li>How can i add this tab so my custom product type can also
  behave like a variable product. </li>
  <li>Screen Shot: <a href="http://prntscr.com/ekogwd" rel="nofollow noreferrer">http://prntscr.com/ekogwd</a> </li>
  <li>And i've to use my custom product type strictly means i cannot change it to variable product type.  </li>
  <li>Is there any hook, action, or filter to add this tab manually to my custom product type "Gift card" using woocommerce?</li>
  </ul></li>
  </ul>