How to find menu id, and guids of existing VS menus.

I have read: https://msdn.microsoft.com/en-us/library/bb165739.aspx which explains how to add a submenu to your own top level menu - in which you have specified your top level menu's "id" and "guid".

I would like to add a sub menu to an existing VS Menu - "Debug->Start Debugging" as per Li's answer here: 

I should mention I am using the CPS project system

To do this, I think I need to find out what the "Parent" guid and id of the "Debug->Start Debugging" menu is so that I can add my submenu to it:

<Menu guid="guidTestCommandPackageCmdSet" id="SubMenu" priority="0x0100" type="Menu"><Parent guid="guidTestCommandPackageCmdSet" id="MyMenuGroup"/><Strings><ButtonText>Sub Menu</ButtonText><CommandName>Sub Menu</CommandName></Strings></Menu>

I have found this page but it didn't list that menu option..

Edit: This example shows someone adding a submenu exactly where I want to add one - but it doesn't tell me how they figured out what the parent menu's id and guid was in the first place and that's what I am more interested in learning.. How do we discover these guids and ids for existing menus..

Many Thanks

Darrell