How do I display a button on a QLabel covered by GstVideoOverlay

I created a QWidget, added a QLabel and a QButton to the QWidget, and then I created the gstreamer pipeline, The d3d11videosink is bound to the QLabel object using the gst_video_overlay_set_window_handle method. Then I set QButton to the top (raise()), but the button is always covered by QLabel. How do I set the QButton so that it appears at the top of the QLabel?