from tkinter import Tk,Label,PanedWindow,BOTH,VERTICAL

master = Tk()
m1 = PanedWindow(master)
m1.pack(fill=BOTH, expand=1)

left = Label(m1, text="left pane")
m1.add(left)

m2 = PanedWindow(m1, orient=VERTICAL)
m1.add(m2)

top = Label(m2, text="top pane")
m2.add(top)

bottom = Label(m2, text="bottom pane")
m2.add(bottom)

master.mainloop()