class Window(QWidget):
    def __init__(self):
        super().__init__()

    def init_gui(self):
        self.layout = QVBoxLayout()
        self.setLayout(self.layout)

        self.new1()
        self.new2()

        self.showMaximized()

    def create_scroll_area(self):
        scroll_area = QScrollArea()
        widget = QWidget()
        scroll_area.setWidget(widget)
        layout = QVBoxLayout()
        widget.setLayout(layout)
        button = QPushButton("Ahoj")
        layout.addWidget(button)
        self.layout.addLayout(layout)

    def new1(self):
        self.create_scroll_area()

    def new2(self):
        self.create_scroll_area()

QLayout::addChildLayout: layout "" already has a parent