如何删除未选中的treeview节点

import tkinter as tk
from tkinter import ttk

def delete_unselected_nodes(tree):
    for item in tree.get_children():
        if not tree.selection_contains(item):
            tree.delete(item)
        else:
            delete_unselected_nodes(tree.item(item)['tree'])

root = tk.Tk()

tree = ttk.Treeview(root)
tree.insert('', 'end', text='Node 1')
tree.insert('', 'end', text='Node 2')
tree.insert('', 'end', text='Node 3')

subtree = tree.insert('', 'end', text='Node 4')
tree.insert(subtree, 'end', text='Subnode 1')
tree.insert(subtree, 'end', text='Subnode 2')

tree.pack()

delete_unselected_nodes(tree)

root.mainloop()