How to add DropdownButton to toolbar Item using xcu for extensions

[Harish1]

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>
	</node>

I have added ControlType property as below

DropdownButton

which resulted in the button to look like dropdown. But i am confused on how to add sub items in this fashion.
Please guide

[Harish1]

For example LibreOffice uses Save DropdownButton under which we have sub items like Save As, Export etc.