How to up add item to listbox (with listvariable)

listbox_2.py

import ctypes
import tkinter


def get_selected(event):
    n = listbox.curselection()  #get index no.
    l["text"] = listbox.get(n)  #set label text

def input(event):
    item_list.append(entry.get())   #add item
    list_var.set(item_list)         #set variable
    entry.delete(0, tkinter.END)    #clear entry


if __name__ == "__main__":
    ctypes.windll.shcore.SetProcessDpiAwareness(1)
    root = tkinter.Tk()

    #label
    l = tkinter.Label(
        root,
        text = "select item",
        width = 15,
        bg = "lightblue",
    )
    l.pack()

    #listobox
    item_list = ["Easy", "Normal", "Hard"]
    list_var = tkinter.StringVar(root, value=item_list)
    listbox = tkinter.Listbox(root, listvariable=list_var)
    listbox.bind("<<ListboxSelect>>", get_selected)
    listbox.pack()

    #entry
    entry = tkinter.Entry(root, bd=5)
    entry.bind("<Return>", input)      #bind Retun key
    entry.pack(pady=3)
    
    root.mainloop()