How to create a dropdown button under issue operations button?

How can I create a custom dropdown in the issue operations section?

I was able to create a button easily using web item and section: transitions-all. How can I make this into a dropdown instead similar to the picture shown.

You can add more web-items e.g in atlassian-plugin.xml
grafik

 <web-item name="25" i18n-name-key="25.name" key="25" section="my-item-link/my-section" weight="1000">
    <description key="25.description">The 25 Plugin</description>
    <label key="25.label"/>
    <link linkId="25-link">http://25.com</link>
  </web-item>
  <web-section name="mySection" i18n-name-key="my-section.name" key="my-section" location="my-item-link" weight="1000">
    <description key="my-section.description">The mySection Plugin</description>
    <!--  label key="my-section.label"/-->
  </web-section>
  <web-item name="my-item" i18n-name-key="my-item.name" key="my-item" section="system.top.navigation.bar" weight="1000">
    <description key="my-item.description">The myItem Plugin</description>
    <label key="my-item.label"/>
    <link linkId="my-item-link">http://customwebitem.de</link>
  </web-item>
  <web-item name="Atlassian Developer Site" i18n-name-key="atlassian-developer-site.name" key="atlassian-developer-site" section="my-item-link/my-section" weight="1000">
    <description key="atlassian-developer-site.description">The Atlassian Developer Site Plugin</description>
    <label key="atlassian-developer-site.label"/>
    <link linkId="atlassian-developer-site-link">http://totsy-dev.tonbeller.com</link>
  </web-item>
  <web-item name="Google" i18n-name-key="google.name" key="google" section="my-item-link/my-section" weight="1000">
    <description key="google.description">The Google Plugin</description>
    <label key="google.label"></label>
    <link linkId="google-link">http://www.google.com</link>
  </web-item>