private function addMongoNode()
    {
        $builder = new TreeBuilder('mongodb');
        $node    = $this->getRootNode($builder, 'mongodb');

        $node
            ->addDefaultsIfNotSet()
            ->children()
                ->scalarNode('connection_id')->defaultNull()->end()
                ->scalarNode('collection_id')->defaultNull()->end()
                ->scalarNode('database_name')->defaultValue('doctrine_cache')->end()
                ->scalarNode('collection_name')->defaultValue('doctrine_cache')->end()
                ->scalarNode('server')->defaultValue('%doctrine_cache.mongodb.server%')->end()
            ->end()
        ;

        return $node;
    }