Add drop down menu TO a page

So I have seen a TON of tutorials for add a menu to a page, but I’m looking to do the opposite. I want to create a drop down menu inside a page.

For example, I’d like users to navigate to a page called ‘catalog’. When they go to this page it will have one drop down menu on this page. When I select an option it will populate another dropdown underneath that that will have a sub menu, and this will happen like 2 or 3 times.

How can I achieve something like this? Will I have to create a page then hard code the HTML in the text view, or is their an easier way? Ideally I’d like to bake this into my theme and not add another plugin. So if there is any legit tutorials to explain this I’d greatly appreciate it.