Creating a multidimensional array using the symfony config tree constructor

I want to create a config for my own node like this:

my_filters:
    filter_type_a:
        - \MyBundle\My\ClassA
        - \MyBundle\My\ClassA2
    filter_type_b:
        - \MyBundle\My\ClassB

      

        
        
        
      

    

my_filters

must be a variable length array and my_filters.filter_type_a

must also be a variable length array.

I tried

$treeBuilder = new TreeBuilder(); 
$rootNode = $treeBuilder->root('my_bundle');
$rootNode
     ->children()
         ->arrayNode('my_filters')
             ->prototype('array')
                 ->prototype('array')
                     ->children()
                         ->scalarNode('my_filters')->end()
                      ->end()
                 ->end()
             ->end()
         ->end()
     ->end()

      

        
        
        
      

    

but I got the following error: Invalid type for path "my_bundle.my_filters.filter_type_a.0". Expected array, but got string

.

This is where I set the config:

class MyBundleExtension extends Extension
{
    public function load(array $configs, ContainerBuilder $container)
    {
        $this->loadServices($container);
        $this->loadConfig($configs, $container);
    }

    private function loadConfig(array $configs, ContainerBuilder $container)
    {       
        $configuration = new Configuration();
        $config = $this->processConfiguration($configuration, $configs);
        $container->setParameter('my_bundle.my_filters', $config['my_filters']);
    }

    private function loadServices(ContainerBuilder $container)
    {
        $loader = new Loader\YamlFileLoader($container, new FileLocator(__DIR__.'/../Resources/config'));
        $loader->load('services.yml');
    }
}

      

        
        
        
      

    

I can't see my mistake, can anyone tell me?