use default_url for logo link

IPython/html/base/handlers.py

@@ -138,6 +138,10 b' class IPythonHandler(AuthenticatedHandler):'
         return self.settings.get('base_url', '/')
 
     @property
+    def default_url(self):
+        return self.settings.get('default_url', '/')
+
+    @property
     def ws_url(self):
         return self.settings.get('websocket_url', '')
 
@@ -238,6 +242,7 b' class IPythonHandler(AuthenticatedHandler):'
     def template_namespace(self):
         return dict(
             base_url=self.base_url,
+            default_url=self.default_url,
             ws_url=self.ws_url,
             logged_in=self.logged_in,
             login_available=self.login_available,

IPython/html/templates/page.html

@@ -83,7 +83,7 b''
 
 <div id="header">
   <div id="header-container" class="container">
-  <div id="ipython_notebook" class="nav navbar-brand pull-left"><a href="{{base_url}}tree" title='dashboard'>{% block logo %}<img src='{{static_url("base/images/logo.png") }}' alt='Jupyter Notebook'/>{% endblock %}</a></div>
+  <div id="ipython_notebook" class="nav navbar-brand pull-left"><a href="{{default_url}}" title='dashboard'>{% block logo %}<img src='{{static_url("base/images/logo.png") }}' alt='Jupyter Notebook'/>{% endblock %}</a></div>
 
   {% block login_widget %}