How to show hot key for menus in .vsct file

Hi All,

I have a following code in .vsct file to create a menu-

<Button guid="guidVSPackage1CmdSet" id="cmdVar" priority="0x0100" type="Button">
        <Parent guid="guidVSPackage1CmdSet" id="ParentGroup"/>
        <CommandFlag>DynamicVisibility</CommandFlag>
        <Strings>
          <ButtonText>CustomVariables</ButtonText>
          <CommandName>&amp;CustomVariables</CommandName>
        </Strings>
      </Button>

I want to show hot key for mentioned command (i.e. for CustomVariable). I used CommandName property already, but in vain.

for example - 

Did I miss anything ? Thanks in advance.

Thanks.