def METHOD_NAME(self, item_id: UUID, parent_id: UUID) -> None:
    """Add a child to an item."""
    try:
        item = self.lookup[item_id]
    except KeyError:
        raise
    try:
        self.data.remove(item)
        self.lookup[parent_id].children.append(item)
        item.METHOD_NAME = self.lookup[parent_id]
        self.emit('parent-change', item, self.lookup[parent_id])
    except KeyError:
        raise