Что сделать чтобы при закрытии главного окна закрывались все остальные?

from PyQt5 import QtCore, QtGui, QtWidgets
import sys
 
class Ui_MainWindow(object):
    def setupUi(self, MainWindow):
        MainWindow.setObjectName("MainWindow")
        MainWindow.resize(400, 400)
        MainWindow.setMinimumSize(QtCore.QSize(400, 400))
        self.centralwidget = QtWidgets.QWidget(MainWindow)
        self.centralwidget.setObjectName("centralwidget")
        self.pushButton = QtWidgets.QPushButton(self.centralwidget)
        self.pushButton.setGeometry(QtCore.QRect(160, 160, 75, 23))
        self.pushButton.setObjectName("pushButton")
        self.pushButton.clicked.connect(self.open)
        MainWindow.setCentralWidget(self.centralwidget)
        self.retranslateUi(MainWindow)
        QtCore.QMetaObject.connectSlotsByName(MainWindow)
 
    def open(self):
        global Dialog
        Dialog = QtWidgets.QDialog()
        ui = Ui_Dialog()
        ui.setupUi(Dialog)
        Dialog.show()
 
 
    def retranslateUi(self, MainWindow):
        _translate = QtCore.QCoreApplication.translate
        MainWindow.setWindowTitle(_translate("MainWindow", "MainWindow"))
        self.pushButton.setText(_translate("MainWindow", "PushButton"))
 
class Ui_Dialog(object):
    def setupUi(self, Dialog):
        Dialog.setObjectName("Dialog")
        Dialog.resize(400, 300)
        self.label = QtWidgets.QLabel(Dialog)
        self.label.setGeometry(QtCore.QRect(200, 140, 47, 13))
        self.label.setObjectName("label")
 
        self.retranslateUi(Dialog)
        QtCore.QMetaObject.connectSlotsByName(Dialog)
 
    def retranslateUi(self, Dialog):
        _translate = QtCore.QCoreApplication.translate
        Dialog.setWindowTitle(_translate("Dialog", "Dialog"))
        self.label.setText(_translate("Dialog", "Окно"))
 
if __name__ == "__main__":
    app = QtWidgets.QApplication(sys.argv)
    MainWindow = QtWidgets.QMainWindow()
    ui = Ui_MainWindow()
    ui.setupUi(MainWindow)
    MainWindow.show()
    sys.exit(app.exec_())

    def open(self):
        global Dialog
        Dialog = QtWidgets.QDialog(self)     # <==
        ui = Ui_Dialog()
        ui.setupUi(Dialog)
        Dialog.show()

    def open(self):
        global Dialog
        Dialog = QtWidgets.QDialog(MainWindow)     # <==
        ui = Ui_Dialog()
        ui.setupUi(Dialog)
        Dialog.show()