def add_client(self, node, hint=None):
        """Add a node below this node

        The `hint` is a node to place the new node after in this nodes
        children.
        """
        node.parent = self
        if hint is not None:
            try:
                idx = self.children.index(hint)
            except ValueError:
                pass
            else:
                self.children.insert(idx + 1, node)
                return
        self.children.append(node)
Add a node below this node

        The `hint` is a node to place the new node after in this nodes
        children.
        
libqtile/layout/tree.py