Creating a multi-level menu drop-down

I want to create a folder within a folder for the navigation menu. This is not possible within Squarespace's normal tools, so I am looking for a solution using code.

As you can see in the below screenshot, we have 9 selection options under Field Guide currently. Instead, I want to change this to 2 options: "The Northeast" and "The South" and then categorize each of the 9 regions under one of these 2 categories. When someone hovers over "The South" for example, it should display "Big Bend Country" and "Texas Hill Country" to the right.

Thanks in advance for the help!

You can add all items to Folder, then we can give code to make folder to 2 columns & bold the titles