How to define dynamic configuration using the TreeBuilder?

I want to configure a bundle to allow different behavior for different companies. The config structure within them will be the same.

My config.yml shall look like this:

bunde_namespace:
    company:
        company_1:
            foo: bar
            baz: poit
        company_2:
            foo: bar
            baz: poit
        company_3:
            ...

When I access the $config I expect the array to look something like this:

$config['company'] = [
    'company_one' => [
        'foo' => 'bar'
        'baz' => 'poit'
    ],
    'company_two' => [
        'foo' => 'bar'
        'baz' => 'poit'
    ],
    ...
];

Yet I have no experience with the TreeBuilder and setting up the configuration as described in the docs and it still eludes me as to how I setup my configuration so that it treats the children of company as keyed arrays.

What I achieved so far is to setup the config for one company, like so:

class Configuration implements ConfigurationInterface
{
    /**
     * {@inheritdoc}
     */
    public function getConfigTreeBuilder()
    {
        $treeBuilder = new TreeBuilder();
        $rootNode = $treeBuilder->root('dreamlines_booking_service_fibos');

        $rootNode
            ->children()
            ->arrayNode('company')
                ->children()
                    ->scalarNode('foo')->end()
                    ->scalarNode('baz')->end()
                    ->end()
                ->end()
        ->end();

        return $treeBuilder;
    }
}

And the simplified config.yml would look like this:

bundle_namespace:
    company:
        foo: bar
        baz: poit

Yet this is not what I want.

I am assuming that I need to use useAttributeAsKey yet I have trouble getting it work.

This fails:

    $rootNode
        ->children()
        ->arrayNode('company')
            ->prototype('array')
            ->useAttributeAsKey('name')
            ->children()
                    ->scalarNode('foo')->end()
                    ->scalarNode('baz')->end()
                ->end()
           ->end()
        ->end()
    ->end();

stating:

[Symfony\Component\Config\Definition\Exception\InvalidDefinitionException] ->useAttributeAsKey() is not applicable to concrete nodes at path "bundle_namespace."

Where am I going wrong?