<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def in_tree(self, name):
 r""" Test if a node is in the tree. :param name: Node name to search for :type name: :ref:`NodeName` :rtype: boolean :raises: RuntimeError (Argument \`name\` is not valid) """

        if self._validate_node_name(name):
            raise RuntimeError("Argument `name` is not valid")
        return name in self._db