[The Twig function](https://github.com/lcharette/UF_MarkdownPages/blob/master/src/Twig/MarkdownPagesTwigExtension.php#L58) currently doesn't accept the [level argument](https://github.com/lcharette/UF_MarkdownPages/blob/master/src/Markdown/MarkdownPagesManager.php#L165) for the tree generation. Once implemented, should also be added to [the doc](https://github.com/lcharette/UF_MarkdownPages/blob/master/docs/SidebarTreeView.md).