code: def add_callback(self, callback):
      self.callbacks.append(callback)
  
imports: from PyQt5 import QtCore, QtGui, QtWidgets, sip
  from PyQt5.QtCore import Qt
  from pandasgui.store import PandasGuiDataFrameStore, PandasGuiStore
  from pandasgui.widgets import base_widgets
  import tempfile
  import os
  from pandasgui.utility import traverse_tree_widget
  from pandasgui.widgets.column_viewer import FlatDraggableTree
  from pandasgui.widgets.json_viewer import JsonViewer
label_desc: Use image node_id 2 for calling the DelayedMimeData obj's underlying member method code with example usage: obj.add_callback(callback) without return types