I want to clarify, the homemade widgets (megawidgets to be precise) Tree and Table are not superfluous in the project. There is indeed TreeView in Tkinter.

It is legitimate to wonder why there is Tree when TreeView already exists. Let's do a little genealogy to get some context before answering.

Well, Tkinter is the standard Python interface to the Tk GUI toolkit. In the face of the competition, Tk guys added a new set of widgets: the famous Tk themed widget (ttk).

It was not just an increment like 1 + 1 = 2 but rather a new direction slightly different from the old one without loss of compatibility of course. This document is great to go deeper in the topic: https://core.tcl-lang.org/tips/doc/trunk/tip/48.md