I'm trying to put some of my builds into a folder but I want to hide them like meepcity?

I'm trying to put certain things in a folder, but on the main map I want the things outside of the mainmap to be hidden, like what meepcity does, I'm trying to figure out a way to script it, but nothing is working, can someone try and help explain to me in a specific way how to do that

What I usually do with things I want to be hidden is that I put them into objects that are not parts(such as a script), that way they don't show up in the workspace, if that's what you mean.