How to take users dynamically from csv in jmeter?

I have requirement as follows ...

The load what we need to have is something like 10 users start at same time, then 20 seconds break and 10 more users (different users) and so on.

For the first time, I can set
users: 10
ramp up period : 0
loop count: 1

how can I set next 10 users which I specified in CSV file after 20 seconds break?

Can anyone explain me the solution for this?

Thanks in advance.