manager dashboard - see all people's tasks under the manager

I am trying to create a dashboard for a director who wants to see not only the info of those she manages, but also the ones below her. 

For example:

Director manages A and B. A manages person 1 and person 2. B manages person 3 and person 4.
The director wants to see info about A, B, as well as person 1, 2, 3, and 4.

Right now, I am only able to see those she manages directly, using the User > Manager ID = $$USER.ID.

I would also like this report to be use-able with other directors down the line.

Is there a way to show in reports (both reports and calendar reports) not only her direct manages, but those below?

It might be a common need so if there’s a plethora of existing resources for this, please let me know!

Thank you!