Load configuration: tree widget state

def load_config(self):
        """Load configuration: tree widget state"""
        expanded_state = self.get_option('expanded_state', None)
        # Sometimes the expanded state option may be truncated in .ini file
        # (for an unknown reason), in this case it would be converted to a
        # string by 'userconfig':
        if is_text_string(expanded_state):
            expanded_state = None
        if expanded_state is not None:
            self.explorer.treewidget.set_expanded_state(expanded_state)