解决方案是让一个类使用Tkinter，另一个使用PyQt5。
然而，虽然这个解决方案确实有效，但它会导致一个重复出现的错误，这并不影响代码本身。您需要通过PyQT5代码调用该类。下面是一个解决方案：

from PySide2.QtCore import *
from PySide2.QtWidgets import *
from PySide2.QtGui import *

from tkinter import *
from tkinter.ttk import Progressbar
from tkinter.ttk import Combobox
from tkinter.ttk import Notebook
from tkinter.ttk import Treeview
from PIL import Image, ImageTk
import tkinter.font


class Widget2():
    def __init__(self, parent):
        self.gui(parent)

    def gui(self, parent):
        if parent == 0:
            self.w2 = Tk()
            self.w2.geometry('130x60')
        else:
            self.w2 = Frame(parent)
            self.w2.place(x = 0, y = 0, width = 130, height = 60)
        self.button1 = Button(self.w2, text = "Button", font = tkinter.font.Font(family = "Calibri", size = 9), cursor = "arrow", state = "normal")
        self.button1.place(x = 20, y = 20, width = 90, height = 22)

class Widget1(QWidget):
    def __init__(self, parent=None):
        super(Widget1, self).__init__(parent)
        self.gui()

    def gui(self):
        self.w1 = self
        self.w1.setAutoFillBackground(True)
        self.w1.setWindowTitle("")
        self.w1.resize(500, 450)
        self.w1.setCursor(Qt.ArrowCursor)
        self.w1.setToolTip("")
        self.button1 = QToolButton(self.w1)
        self.button1.setSizePolicy(QSizePolicy.Expanding, QSizePolicy.Fixed)
        self.button1.setText("Button")
        self.button1.move(9, 214)
        self.button1.resize(482, 22)
        self.button1.setCursor(Qt.ArrowCursor)
        self.button1.setToolTip("")
        self.button1.clicked.connect(self.event)
        return self.w1

    def event(self):
        b = Widget2(0)
        b.w2.mainloop()

if __name__ == '__main__':
    import sys
    app = QApplication(sys.argv)
    a = Widget1()
    a.show()
    sys.exit(app.exec_())