Parasite, Levels of Understanding

The movie Parasite won Best Picture 2020. Not sure I agree, but I could probably say that about many Best Pictures over previous years.

I'm not trying to say it isn't a good movie, it was.

Perhaps, I am not understanding all of its layers and levels. The half basement, the deep basement, the main level, upstairs, and all of the levels in between.

Who do you suppose are/is the parasitic one(s)? Who feeds off of whom?

And that ending; it really takes the cake.