How to add a custom dropdown box in admin category page?

[bkprestashop]

Hello devs, 

I have been trying to figure out how to add custom fields into the category page in admin office. Based on my findings so far, using the HookActionCategoryFormBuilderModifier is the proper way to modify existing forms. However, based on the documentation here, https://devdocs.prestashop.com/1.7/development/components/form/types-reference/, it does not seem to have a "DropDownType". Is there a way to add a custom dropdown field by doing this? If not, is there another way to achieve what I'm trying to do?

Any help is sincerely appreciated!