我试图用wxPython创建一个按钮，但是它没有出现在输出框中，我哪里错了？

import wx

class MyFrame(wx.Frame):
    def __init__(self):
        super().__init__(None, title="Button Example")
        
        panel = wx.Panel(self)
        sizer = wx.BoxSizer(wx.VERTICAL)
        
        button = wx.Button(panel, label="Click Me")
        button.Bind(wx.EVT_BUTTON, self.on_button_click)
        
        sizer.Add(button, 0, wx.ALIGN_CENTER|wx.ALL, 5)
        panel.SetSizer(sizer)
        
    def on_button_click(self, event):
        print("Button clicked!")
        
app = wx.App()
frame = MyFrame()
frame.Show()
app.MainLoop()