When creating a menu in Python 3.6 and tkinter, drop down doesnt stay in Frame

Edit: OS is Windows 10 64 Bit

Ok, so I have googled my rear-end off on this one. I am building a simple tkinter app and upon setting it up and just generally messing around with options to add to it, my drop down from the menu created doesn’t stay constrained inside the Frame.

import tkinter as tk


class Window(tk.Frame):

    def __init__(self, master=None):
        super().__init__(master)
        self.master = master
        self.main_window()
        self.widgets()

    # All main window parameters go here
    def main_window(self):
        self.master.title("Calculate Commission")
        self.master.geometry("800x600")
        self.pack()

    def widgets(self):
        main_menu = tk.Menu(self.master, tearoff=0)
        self.master.config(menu=main_menu)

        # Create File Menu and Drop Down
        file = tk.Menu(main_menu, tearoff=0)
        file.add_command(label="Save")
        file.add_command(label="Exit", command=exit)
        main_menu.add_cascade(label="File", menu=file)

        # Create Edit Menu and Drop Down
        edit = tk.Menu(main_menu, tearoff=0)
        edit.add_command(label="undo")
        main_menu.add_cascade(label="Edit", menu=edit)


main = tk.Tk()
comm_prog = Window(master=main)
main.mainloop()

Please see this attached screenshot to see what I am referring too:

I am fairly confident this may end up either of two ways. Either it’s a rookie mistake I am making somewhere, or its system dependent and its just specific to my computer for some reason. If anyone has any insight, I would greatly appreciate it.

Adding screenshot of Tcl Version: