Subcategorys display in search bar

hi, i need your help.
i wonder if it’s possible to show subcategory only after parent category choice in main search bar on the homepage of supreme directory theme. something like menu and sub-menu items(where the sub-menu items appears only when you point your mouse on parent menu item).
i have a category with more than 500 subcategory and, unfortunately, is the first that appear on the categorys selection. So to view the other categorys you have to scroll down more than 500 items…
if not possible, can i hide the subcategorys (only in the search bar)? any suggest will be appreciate… thank you