Select2 optgroup scroll problem

I would like to use select2 with optgroup however current user experience is not usable.
As you can see in the link, every optgroup has own seperated scroll (scroll2) and also option wrapper has own scroll (scroll1). In the select2 demo (https://select2.org/appearance#labels) does not like this. Do you have an any suggestion to use select2 optgroups without group scrolls like select2 demo?

Current SS: https://imgur.com/Juxaemy
Expected SS: https://imgur.com/e4EtsPn
POC Code: https://pastebin.pl/view/b1809022
Version: Metronic: v8.0.38