使用Notebook在Tkinter Python中创建标签会导致框架收缩

import tkinter as tk
from tkinter import ttk

root = tk.Tk()

notebook = ttk.Notebook(root)
notebook.pack(fill='both', expand=True)

frame1 = ttk.Frame(notebook)
frame1.pack(fill='both', expand=True)
notebook.add(frame1, text='Tab 1')

label1 = ttk.Label(frame1, text='Label 1')
label1.pack()

frame2 = ttk.Frame(notebook)
frame2.pack(fill='both', expand=True)
notebook.add(frame2, text='Tab 2')

label2 = ttk.Label(frame2, text='Label 2')
label2.pack()

notebook.pack_propagate(False)  # 禁止Notebook自动调整大小

root.mainloop()