如何在PyQt5中的主窗口顶部显示新窗口

from PyQt5.QtWidgets import QApplication, QMainWindow, QLabel, QPushButton

class MainWindow(QMainWindow):
    def __init__(self):
        super().__init__()
        self.setWindowTitle("主窗口")
        self.setGeometry(100, 100, 400, 300)

class MainWindow(QMainWindow):
    def __init__(self):
        super().__init__()
        self.setWindowTitle("主窗口")
        self.setGeometry(100, 100, 400, 300)

        self.button = QPushButton("打开新窗口", self)
        self.button.clicked.connect(self.open_new_window)
        self.button.setGeometry(10, 10, 120, 30)

    def open_new_window(self):
        new_window = QLabel("新窗口", self)
        new_window.setGeometry(50, 50, 200, 100)
        new_window.show()

if __name__ == "__main__":
    app = QApplication([])
    main_window = MainWindow()
    main_window.show()
    app.exec_()