code: def show_tree(model=None):
      
      if model is None:
          model = mx.cur_model()
      view = get_modeltree(model)
      app = QApplication.instance()
      if not app:
          raise RuntimeError("QApplication does not exist.")
      view.show()
      app.exec_()
docs: Display the model tree window.
  
      Args:
          model: :class:`Model <modelx.core.model.Model>` object.
              Defaults to the current model.
  
      Warnings:
          For this function to work with Spyder, *Graphics backend* option
          of Spyder must be set to *inline*.