diff --git a/core/includes/menu.inc b/core/includes/menu.inc
index 12d2a23..f8d53a5 100644
--- a/core/includes/menu.inc
+++ b/core/includes/menu.inc
@@ -342,7 +342,6 @@ function template_preprocess_menu_tree(&$variables) {
   if (!isset($variables['attributes']['class'])) {
     $variables['attributes']['class'] = array();
   }
-  $variables['attributes']['class'][] = 'menu';
 
   $variables['tree'] = $variables['tree']['#children'];
 }
diff --git a/core/modules/system/templates/menu-tree.html.twig b/core/modules/system/templates/menu-tree.html.twig
index 03acca6..6eba929 100644
--- a/core/modules/system/templates/menu-tree.html.twig
+++ b/core/modules/system/templates/menu-tree.html.twig
@@ -34,7 +34,7 @@
       <h2{{ heading.attributes }}>{{ heading.text }}</h2>
     {%- endif -%}
   {%- endif -%}
-  <ul{{ attributes }}>
+  <ul{{ attributes.addClass('menu') }}>
     {{ tree }}
   </ul>
 {%- endif %}
diff --git a/core/themes/bartik/templates/menu-tree.html.twig b/core/themes/bartik/templates/menu-tree.html.twig
new file mode 100644
index 0000000..1f9a7f3
--- /dev/null
+++ b/core/themes/bartik/templates/menu-tree.html.twig
@@ -0,0 +1,40 @@
+{#
+/**
+ * @file
+ * Default theme implementation for a menu tree.
+ *
+ * Available variables:
+ * - attributes: Attributes for the UL containing the tree of links.
+ * - tree: Menu tree to be output.
+ * - heading: (optional) A heading to precede the links.
+ *   - text: The heading text.
+ *   - level: The heading level (e.g. 'h2', 'h3').
+ *   - attributes: (optional) A keyed list of attributes for the heading.
+ *   If the heading is a string, it will be used as the text of the heading and
+ *   the level will default to 'h2'.
+ *
+ *   Headings should be used on navigation menus and any list of links that
+ *   consistently appears on multiple pages. To make the heading invisible use
+ *   the 'visually-hidden' CSS class. Do not use 'display:none', which
+ *   removes it from screen-readers and assistive technology. Headings allow
+ *   screen-reader and keyboard only users to navigate to or skip the links.
+ *   See http://juicystudio.com/article/screen-readers-display-none.php and
+ *   http://www.w3.org/TR/WCAG-TECHS/H42.html for more information.
+ *
+ * @see template_preprocess_menu_tree()
+ *
+ * @ingroup themeable
+ */
+#}
+{% if tree -%}
+  {%- if heading -%}
+    {%- if heading.level -%}
+      <{{ heading.level }}{{ heading.attributes }}>{{ heading.text }}</{{ heading.level }}>
+    {%- else -%}
+      <h2{{ heading.attributes }}>{{ heading.text }}</h2>
+    {%- endif -%}
+  {%- endif -%}
+  <ul{{ attributes.addClass('menu', 'clearfix') }}>
+    {{ tree }}
+  </ul>
+{%- endif %}