Кнопки в строке состояния

from PyQt5 import QtCore, QtWidgets
from PyQt5.QtWidgets import QMdiArea, QStatusBar, QPushButton
 
class Ui_MainWindow(object):
    def setupUi(self, MainWindow):
        MainWindow.setObjectName("MainWindow")
        MainWindow.resize(300, 200)
        self.centralwidget = QtWidgets.QWidget(MainWindow)
        self.centralwidget.setObjectName("centralwidget")
 
        self.mdiArea = QtWidgets.QMdiArea(self.centralwidget)
        self.mdiArea.setFrameShape(QtWidgets.QFrame.Box)
        self.mdiArea.setObjectName("mdiArea")
        
        
        MainWindow.setCentralWidget(self.mdiArea)
        
        self.menubar = QtWidgets.QMenuBar(MainWindow)
        self.menubar.setGeometry(QtCore.QRect(0, 0, 800, 21))
        self.menubar.setObjectName("menubar")
 
        self.menu_1 = QtWidgets.QMenu(self.menubar)
        self.menu_1.setObjectName("menu_1")
                
        MainWindow.setMenuBar(self.menubar)
 
        self.statusbar = QStatusBar(MainWindow)
        self.statusbar.setAutoFillBackground(False)
        self.statusbar.setObjectName("statusbar")
       
        MainWindow.setStatusBar(self.statusbar)
 
    
        self.pop_menu = QtWidgets.QAction(MainWindow)
        self.pop_menu.setObjectName("pop_menu")
        
        self.menu_1.addAction(self.pop_menu)
        self.menubar.addAction(self.menu_1.menuAction())
                    
        self.retranslateUi(MainWindow)
        QtCore.QMetaObject.connectSlotsByName(MainWindow)
 
        self.pop_menu.triggered.connect(self.wnd_1)
         
    def retranslateUi(self, MainWindow):
        _translate = QtCore.QCoreApplication.translate
        MainWindow.setWindowTitle(_translate("MainWindow", "FFF"))
        self.menu_1.setTitle(_translate("MainWindow", "menu_1"))
        self.pop_menu.setText(_translate("MainWindow", "pop_menu"))
 
class MyWin(QtWidgets.QMainWindow, Ui_MainWindow):
    def __init__(self):
        super().__init__()
        self.setupUi(self)
               
    def wnd_1(self):
        
        self.sub = QtWidgets.QMdiSubWindow()
        
        self.sub.setWindowTitle("wnd_1")        
        self.mdiArea.addSubWindow(self.sub)
        self.mdiArea.cascadeSubWindows()
        self.sub.show()
 
        self.btn_wnd_1 = QPushButton('wnd_1', self.statusbar)
        self.btn_wnd_1.setObjectName('wnd_1')
        self.statusbar.addWidget(self.btn_wnd_1)
     
    
 
if __name__ == "__main__":
    import sys
    app = QtWidgets.QApplication(sys.argv)
    w = MyWin()
    w.show()
    sys.exit(app.exec_())

        self.btn_wnd_1 = QPushButton('wnd_1', self.statusbar)
        self.btn_wnd_1.setObjectName('wnd_1')
        self.btn_wnd_1.setMinimumSize(QtCore.QSize(1, 0))
        self.statusbar.addWidget(self.btn_wnd_1)