code: def insert(self, parent, index, iid=None, **kw):
          
          self._visual_drag.insert(parent, index, iid, **kw)
          return ttk.Treeview.insert(self, parent, index, iid, **kw)
docs: Creates a new item and return the item identifier of the newly created item.
          
          :param parent: identifier of the parent item
          :type parent: str
          :param index: where in the list of parent's children to insert the new item
          :type index: int or "end"
          :param iid: item identifier, iid must not already exist in the tree. If iid is None a new unique identifier is generated.
          :type iid: None or str
          :param kw: item's options: see :meth:`~Table.item`
          
          :return: the item identifier of the newly created item
          :rtype: str