How to have tabs of a ttk Notebook in different rows?
It is not possible with ttk to do this and it is a horrible design anyway. Instead, create an "options dialog" where you put either a list or a treeview in a panel on the side and use that to select among your many subpages. You can then use a notebook without tabs or simply switch in different frames containing your child pages in response to clicks on the selection pane.
Search google images for "options dialog" to see any number of implementations of this scheme. Multiple rows of tabs is a really bad design from a usability perspective.
I offer this link to the Hall of Shame to discourage anyone from considering mutiple rows on a tabbed dialog.