Multiple select for multiple groups

Question

We have a set of devices that belong to different groups. Each device generates multiple time-series data streams that can be visualised. All devices in the same group have same data streams.

For example:
Group 1:
    Devices:
        Device 1
        Device 2
        Device 3
    Streams
        Stream 1
        Stream 2
        Stream 3
Group 2:
    Devices:
        Device 1
        Device 2
    Streams
        Stream 1
        Stream 2

A user can select devices from each group with their streams. What would be the best way to let a user navigate through such selection?

Presently, we're thinking for two dropdowns for each category, one for devices and the other for streams.

Answer 1

As thinking the behavior of multiple selection, I got inspiration from Windows or MacOS file selection, it's a familiar experience for user. The challenge is how to present the three levels structure as an easy understanding layout. I simulate the layout as below:

Answer 2

I guess the "normal way" is to select a device and then select it's streams. This way implies that each device has checkboxes associated, then when a stream is already assigned it should disappear from the other device's checkboxes, and it gets complex.

An easier way would be to assign a dropdown of devices to each stream; as each stream can belong only one device, but each device can have several streams. This way is much easier but makes the selection from, what I suspect would be, the last point.