Pyside QTreeWidget with custom widget items disappear on drop

Question

I am tyring to put together a QTreeWidget UI that uses custom widgets as its items. I want to be able to drag and drop to rearrange the items in the tree. I am finding that, on drop, the custom widgets are getting lost. How can I make this work? Thanks.

Simplified code example below:

from PySide6 import QtWidgets, QtCore

class CustomWidgetItem(QtWidgets.QWidget):
    def __init__(self, label_text, parent=None):
        super(CustomWidgetItem, self).__init__(parent)
        self.layout = QtWidgets.QHBoxLayout(self)
        self.label = QtWidgets.QLabel(label_text)
        self.button = QtWidgets.QPushButton("Custom Button")
        self.button.clicked.connect(self.btn_click)
        self.layout.addWidget(self.label)
        self.layout.addWidget(self.button)
        self.setLayout(self.layout)

    def btn_click(self):
        print(self.label.text())

class CustomTreeWidget(QtWidgets.QTreeWidget):
    def __init__(self, parent=None):
        super(CustomTreeWidget, self).__init__(parent)
        self.setHeaderHidden(True)
        self.setDragEnabled(True)
        self.setDragDropMode(QtWidgets.QTreeView.InternalMove)

    def dropEvent(self, event):
        source = event.source()
        if isinstance(source, QtWidgets.QTreeWidget):
            super().dropEvent(event)
        else:
            event.setDropAction(QtCore.Qt.MoveAction)
            event.accept()

class MainWindow(QtWidgets.QWidget):
    def __init__(self, parent=None):
        super(MainWindow, self).__init__(parent)
        self.setWindowTitle("Custom Tree Widget")
        self.layout = QtWidgets.QVBoxLayout(self)
        self.tree_widget = CustomTreeWidget()
        self.layout.addWidget(self.tree_widget)
        self.add_items()

    def add_items(self):
        for i in range(5):
            child_item = QtWidgets.QTreeWidgetItem(self.tree_widget, ['Group %d' % i])
            custom_widget_item = QtWidgets.QTreeWidgetItem(child_item)
            custom_widget = CustomWidgetItem('Item %d' % i)
            # set widget
            self.tree_widget.setItemWidget(custom_widget_item, 0, custom_widget)

if __name__ == '__main__':
    app = QtWidgets.QApplication([])
    window = MainWindow()
    window.show()
    app.exec()