def start_subtree(self, conn_type):
        if len(self.children) == 1:
            self.connector = conn_type
        elif self.connector != conn_type:
            self.children = [self._new_instance(self.children, self.connector,
                    self.negated)]
            self.connector = conn_type
            self.negated = False

        self.subtree_parents.append(self.__class__(self.children,
                self.connector, self.negated))
        self.connector = self.default
        self.negated = False
        self.children = []
Sets up internal state so that new nodes are added to a subtree of the
dataset/ETHPy150Open AppScale/appscale/AppServer/lib/django-1.4/django/utils/tree.py/Node.start_subtree