Fetch data from firebase database

Question

I have structure of database like this:

Imgur image link

In database I have lot of customers and I know how to import Customer count and single value ViewModel but I need a count of all ViewModel. For example: I have 5 customers and each have one assigned employee. I would like to receive count of employee - in this examlpe Assigned employee

My code to import Customer count:

Assigned employee

Thanks!