from tkinter import *
from tkinter import ttk
root = Tk()
root.title('Test')
root.iconbitmap()           
PW = ttk.PanedWindow(root, orient=HORIZONTAL)
PW.pack(fill=BOTH, expand=True)

def my_cfm():
    my_label = label(f2,bg=red)
    my_label.pack()

f1 = ttk.Frame(PW, width=75, height=300, relief=SUNKEN)
f2 = ttk.Frame(PW, width=400, height=300, relief=SUNKEN)
PW.add(f1, weight=0)
PW.add(f2, weight=4)
tv = ttk.Treeview(f1)
tv.pack()
tv.insert('', '0', 'item1', text='PRODUCT')

tv.insert('item1', '0', 'A', text='A')

tv.insert('item1', '1', 'B', text='B')
tv.insert('item1', '2', 'C', text='C')
tv.insert('item1', '3', 'D', text='D')
tv.insert('', '1', 'item2', text='REPORTS')

tv.insert('', '3', 'item3', text='QUERIES')
tv.config(height=100)

root.state('zoomed')

tv.mainloop()