import tkinter as tk 
from tkinter import ttk   

root=tk.Tk()

main=ttk.Frame(root)
main.pack(side='left',fill='both',expand=True)

tk.Label(main,text='Label 1 ',bg="green").pack(side="top",fill='both',expand=True)
tk.Label(main,text='Label 2 ',bg="red").pack(side="top",fill='both',expand=True)
tk.Label(root,text='Label left',bg='blue').pack(side='left',expand=True,fill='both')

root.mainloop()