Creating a Cascading Vertical Main Menu

[rdivingdog20]

I'd like to change the layout of my main menu. Under the "Features" menu option, when I created subpages, the menu became horizontal rather than vertical. https://orca3d.com/

Is there a way to make the menu open up cascading like the example below? I don't want the horizontal layout it has defaulted to. Also- "Design" and "Analysis" are behaving as hyperlinks, and they just need to be headers. Any guidance would be greatly appreciated.