How to use the asdf.treeutil.walk_and_modify function in asdf

validate : bool
            When `True` (default) validate the resulting tree.
        """
        type_index = self.type_index

        if not type_index.has_hook(hookname):
            return

        def walker(node):
            hook = type_index.get_hook_for_type(hookname, type(node),
                                                self.version_string)
            if hook is not None:
                return hook(node, self)
            return node
        tree = treeutil.walk_and_modify(self.tree, walker)

        if validate:
            self._validate(tree)
        self._tree = tree
        return self._tree

def custom_tree_to_tagged_tree(tree, ctx):
    """
    Convert a tree, possibly containing custom data types that aren't
    directly representable in YAML, to a tree of basic data types,
    annotated with tags.
    """
    def walker(node):
        tag = ctx.type_index.from_custom_type(type(node), ctx.version_string)
        if tag is not None:
            return tag.to_tree_tagged(node, ctx)
        return node

    return treeutil.walk_and_modify(tree, walker)