How to add a child to Packages using code and in studio?

In the Game Explorer tab in Studio (where you can add a PLACE using Studio, not the Roblox website), it has a section in it called Packages.

I want to know how I can add Models there, not just using code, but adding it in the regular, old Roblox Studio.

By "code" I mean something like this:

local Model = Instance.new("Model", game.Packages)
Model.Name = "Test"

UPDATE: I know how to add packages without using code, but with code...?

This is only to add a package without using code.

Right-click on a model and press "Convert to package...". Once you've done that, go to the Game Explorer tab and click the refresh button. Then, your model should appear as a package inside the Packages folder in the Game Explorer tab.