Any menu can have A/B menu.
You can create A/B menu by clicking A/B icon on menu in the list. This will create duplicate of menu with all items and will place it under menu in list.
Also you can delete this A/B menu by clicking cross icon for this A/B menu.
After creating A/B menu some new configurations will be available in base menu (you can edit them by clicking Edit icon in base menu):
if the conditions are met (site language exists in confiuguraton list and A/B test detected user by cookie) A/B menu will be shown to user.