Simple XML SiteMap for Umbraco 9

XmlSitemap.cshtml

@inherits Umbraco.Cms.Web.Common.Views.UmbracoViewPage
@{ Layout = null; 
    Context.Response.ContentType = "text/xml"; 
}
<?xml version="1.0" encoding="UTF-8" ?>
@{ var selection = Model.Root(); }
<urlset xmlns="http://www.sitemaps.org/schemas/sitemap/0.9">
    <url>
        <loc>@Model.Parent.Url()</loc>
        <changefreq>monthly</changefreq>
        <priority>0.8</priority>
    </url>
    @* Render the sitemap by passing the root node to the traverse helper, below *@
    @{ Traverse(selection); }
</urlset>


@* Helper method to traverse through all descendants *@
@{
    void Traverse(IPublishedContent node)
    {
        const int maxLevelForSitemap = 4;
        var selection = node.Children().Where(x => x.IsVisible() && x.Level <= maxLevelForSitemap).ToArray();

        @* If any items are returned, render a list *@
        if (selection.Length > 0)
        {
            foreach (var item in selection)
            {
                if (@item.Level == 3)
                {
                    <url>
                        <loc>@item.Url()</loc>
                        <changefreq>monthly</changefreq>
                        <priority>0.8</priority>
                    </url>
                }
                Traverse(item);
            }
        }
    }
}