Hi Kurai, and Welcome to Bytes!
A combo box cannot have subsections, so what you ask cannot be done with one combo on its own. It is possible to use multiple combo boxes to do so, where the outermost represents the top-level choice and the innermost represent progressively finer detail layers. We have an insights article on this topic which may help you - see
Cascading Combo/List Boxes for the details.
It is possible to use a different form of control to store tree-structured lists. There is an ActiveX tree control available for this purpose. Its use is by no means simple, however, and unless you have developed a good level of programming expertise to be able to populate the tree details yourself via code I would not recommend you consider such an approach.
-Stewart