Symfony, CMS tutorial, do not understand where is my mistake

[gintare]

I am following online tutorial for Symfony CMS: http://symfony.com/doc/master/cmf/tutorial/introduction.ht ml

I am getting the error:
An exception has been thrown during the rendering of a template ("The menu "main" is not defined.") in src\Acme\BasicC msBundle\Resour ces\views\Defau lt\page.html.tw ig at line 4.
500 Internal Server Error - Twig_Error_Runt ime
1 linked Exception:
InvalidArgument Exception »


I am on the page about menu
http://symfony.com/doc/master/cmf/tutorial/the-frontend.html


Where is the mistake?

<?php

// src/Acme/BasicCmsBundle/DataFixtures/PHPCR/LoadPageData.php
namespace Acme\BasicCmsBundle\DataFixtures\PHPCR;

use Acme\BasicCmsBundle\Document\Page;
use Doctrine\Common\DataFixtures\FixtureInterface;
use Doctrine\Common\Persistence\ObjectManager;
use Doctrine\ODM\PHPCR\DocumentManager;

class LoadPageData implements FixtureInterface
{
    public function load(ObjectManager $dm)
    {
        if (!$dm instanceof DocumentManager) {
            $class = get_class($dm);
            throw new \RuntimeException("Fixture requires a PHPCR ODM DocumentManager instance, instance of '$class' given.");
        }

        $parent = $dm->find(null, '/cms/pages');
        
        $rootPage = new Page();
        $rootPage->setTitle('main');
        $rootPage->setParentDocument($parent);
        $dm->persist($rootPage);        

        $page = new Page();
        $page->setTitle('Home');
        //$page->setParentDocument($parent);
        $page->setParentDocument($rootPage);
        $page->setContent(<<<HERE
Welcome to the homepage of this really basic CMS.
HERE
        );

        $dm->persist($page);
        
        $page = new Page();
        $page->setTitle('About');
        $page->setParentDocument($rootPage);
        $page->setContent(<<<HERE
This page explains what its all about.
HERE
        );
        $dm->persist($page);
        
        $dm->flush();
    }
}

{# src/Acme/BasicCmsBundle/Resources/views/Default/page.html.twig #}
<h1>{{ page.title }}</h1>

{{ knp_menu_render('main') }}

<p>{{ page.content|raw }}</p>
<h2>Our Blog Posts</h2>
<ul>
    {% for post in posts %}
        <li><a href="{{ path(post) }}">{{ post.title }}</a></li>
    {% endfor %}
</ul>