I don't think that component would work as you want it to - it's used to display categories and structures of data to select an individual item, not for selecting the higher level categories. So in this case hovering on a purple item isn't making a choice it's showing the actual choices (green)
I think of it like a file picker - it'll show you the folders but you can't pick a folder, only a file.
You could write your own nested set of listpicker components and dynamically drive the data through that - not a trivial amount of work but it'd be possible
Might be easier to understand if you can share your use case and why the purple items should be selectable?
I want to be able to choose e.g Aursnes, which is a real estate brand -> Sykkylven is therefore an office under that brand.
Further on, if I can pick Aurnes or Sykkylven I have information that I want to show for each brand or office. Maybe I want to show the name of the brand or employees for the office, but in another component.