Which Select2 option displays dropdown items vertically

How Do I...
#1

Hi Everyone,
By default, my select2 control is displaying items horizontally which does not suite my purpose. I wish to load the items grouped and displayed vertically.

I will greatly appreciate your assistance.

Thanks in advance

#2

Any one, please! I have the same issue!

#3

.select2-results__options{display:block}

Finally figured it out.