I investigated problem and found that in ttk.py, Treeview.insert(... iid=None, ...) in method's body has a check:if iid:res = self.tk.call(self._w, "insert", parent, index,"-id", iid, *opts)else:res = self.tk.call(self._w, "insert", parent, index, *opts)It means that if iid is "True" then use it else autogenerate it.Maybe there should be "if iid is not None", not "if iid"? Or there are some reasons to do check this way?