如何在QGraphicsView中制作2层？

from PyQt5.QtWidgets import QApplication, QGraphicsScene, QGraphicsView, QGraphicsRectItem, QGraphicsEllipseItem, QGraphicsTextItem, QGraphicsItemGroup
from PyQt5.QtCore import Qt
import sys

if __name__ == '__main__':
    app = QApplication(sys.argv)

    # 创建底层图层
    scene = QGraphicsScene()

    # 创建底层图形项
    rect = QGraphicsRectItem(0, 0, 100, 100)
    ellipse = QGraphicsEllipseItem(50, 50, 100, 100)
    text = QGraphicsTextItem("Bottom Layer")

    # 将底层图形项添加到底层图层
    scene.addItem(rect)
    scene.addItem(ellipse)
    scene.addItem(text)

    # 创建顶层图层
    group = QGraphicsItemGroup()

    # 创建顶层图形项
    rect2 = QGraphicsRectItem(200, 200, 100, 100)
    ellipse2 = QGraphicsEllipseItem(250, 250, 100, 100)
    text2 = QGraphicsTextItem("Top Layer")

    # 将顶层图形项添加到顶层图层
    group.addToGroup(rect2)
    group.addToGroup(ellipse2)
    group.addToGroup(text2)

    # 将顶层图层添加到底层图层
    scene.addItem(group)

    # 创建QGraphicsView对象，并设置场景
    view = QGraphicsView(scene)

    # 设置视口大小和位置
    view.setSceneRect(0, 0, 400, 400)

    # 显示视图
    view.show()

    sys.exit(app.exec_())