How do use Plan Scope field in a RTC Plan to show work items for specific category and its sub-categories?

 I want to filter the work items in a plan to show the work items filedAgainst a specific category and its sub-categories. 

But none of the above gives me work items fieldAgainst the sub-categories (e.g. "Category A.1").

It only shows the work items fieldAgainst "Category A".

Does any one know how to use Plan Scope to give the work items for category and its sub-categories?

Is it possible to add more than one condition in Plan Scope field. e.g. fieldAgainst:"Category A" OR fieldAgainst:"Category A.1" ?

Is there any other option to get the work items for a Category and its sub-categories in a Plan ?

Thanks