def set_unique_child_node(self, name, node):
try:<EOL><INDENT>temp = self._nodes[name]<EOL>raise RuntimeError("<STR_LIT>" % name)<EOL><DEDENT>except KeyError:<EOL><INDENT>pass<EOL><DEDENT>self.set_child_node(name, node)<EOL>
Add one child node to this node.

Args:
    name (str): Name of the child.
    node (TreeMapNode): Node to add.

Note:
    The name must **not** be in use.