customUI14.xml

<customUI xmlns="http://schemas.microsoft.com/office/2009/07/customui">
   <contextMenus>
      <contextMenu idMso="ContextMenuCell">
         <button id="MyButton" label="Say It"
             insertBeforeMso="Cut" 
             onAction="SayIt" 
             image="avatar"/>
         <menu id="MySubMenu" label="Case Menu" insertBeforeMso="Cut"  >
            <button id="Menu1Button1" label="Upper Case" 
               imageMso="U" onAction="UpperMacro"/>
            <button id="Menu1Button2" label="Lower Case" 
               imageMso="L" onAction="LowerMacro"/>
            <button id="Menu1Button3" label="Proper Case" 
               imageMso="P" onAction="ProperMacro"/>
         </menu>
        <menuSeparator id="MySeparator" insertBeforeMso="Cut" />
      </contextMenu>
   </contextMenus>
</customUI>