If you don't create a root window, tkinter will create one for you when you try to create any other widget. Thus, in your
__init__, because you haven't yet created a root window when you initialize the frame, tkinter will create one for you. Then, you call
make_widgets which creates a second root window. That is why you are seeing two windows.
A well-written tkinter program should always explicitly create a root window before creating any other widgets.
When you modify your code to explicitly create the root window, you'll end up with one window with the expected title.
from tkinter import Tk, Button, Frame, Entry, END
self.parent = parent
# don't assume that self.parent is a root window.
# instead, call `winfo_toplevel to get the root window
# this adds something to the frame, otherwise the default
# size of the window will be very small
label = Entry(self)
root = Tk()
abc = ABC(root)
Also note the use of
self.make_widgets() rather than
ABS.make_widgets(self). While both end up doing the same thing, the former is the proper way to call the function.