Select Category Dropdown

I’ve searched through and can’t find a widget or plugin that fits what I need.

I have my posts categorized by use (ex: category – Fashion, sub-categories – wedding, birthday, etc) with a category drop down list on the side bar. But many of our visitors may be looking for use by topic (ex: category – Wedding subcategories – fashion, decor).

I have categories as a dropdown on my sidebar as the first example above. I’m looking for a widget or plugin that will allow me to also create either a sidebar or put at the top of the page a dropdown that either 1) shows a heading of “wedding” and I am able to choose all of the subcategories to show under it, even if they’re on the site under a different category & just set up as many as I need topics for or 2) one that allows me to pick several topics and multiple dropdowns below them.

This is how it’s set up now:
Fashion:
Wedding
Birthday
Corporate events
Decor:
Wedding
Birthday
Corporate Events

That’s how my categories are set up.

I want to add a dropdown that says:
Weeding:
Fashion
Decor
Birthday
Fashion
Decor
Themes

And just pull the existing subcategories to feed to it, if that makes sense.