Proper way to design desktop application

I am designing desktop application using Python tkinter. I have a menu bar called "Customer" and it contains menu items "new customer", "update customer", and "delete customer". When user clicks on any of the menu items, I want to display only that specific form.

I came up with these:

1. Design each form on frame
2. When user click on any item, display only that form and hide rest
3. This is happening inside the root window (master window)

or

1. Design each form on new top-level window
2. When user clicks on any item, a new window will open
3. Root window (master window) is left running

Which is the standard thing to do?