Help: How to add DropdownButton to toolbar Item using xcu for extensions

Hi Team,
I am a starter and want to know on How to add a drop down button with sub
items (buttons or Text) using the xcu file that we give while creating an
extension. My xcu file for toolbar items looks like below

<node oor:name="OfficeToolBar">
        <node oor:name="org.libreoffice.example.StarterProject.toolbar"
oor:op="replace">
            <prop oor:name="Title" oor:type="xs:string">
                <value>Starter Project</value>
            </prop>
            <node oor:name="t01" oor:op="replace">
                <prop oor:name="URL" oor:type="xs:string">

<value>service:org.libreoffice.example.StarterProject?actionOne</value>
                </prop>
                <prop oor:name="Target" oor:type="xs:string">
                    <value>_self</value>
                </prop>
                <prop oor:name="Context" oor:type="xs:string">
<value>com.sun.star.text.TextDocument,com.sun.star.sheet.SpreadsheetDocument</value>
                </prop>
                <prop oor:name="Title" oor:type="xs:string">
                    <value xml:lang="en-US">Action One</value>
                </prop>
        </node>

I have added ControlType property as below
<prop oor:name="ControlType" oor:type="xs:string">
      <value>DropdownButton</value>
</prop>
 which resulted in the button to look like dropdown. But i am confused on
how to add sub items in this fashion. Please guide
Please guide
https://ask.libreoffice.org/en/question/241346/how-to-add-dropdownbutton-to-toolbar-item-using-xcu-for-extensions/




-- 
Best Regards,
Harish Kumar.B