How do I create sets of geometry?

I have geometry composed of data in branches and sub-branches… But I wan’t to manipulate the geometry as a whole… How can I do that? I’m probably doing something wrong… I tried flatteing but then ’ data conversion fails from text to geometry"…

From what I can barely gather from your screenshot, you probably are fine transforming them separately.
You error may NOT have anything to do with transforming discrete objects as a singular whole.