django-restframework serialize relations as dictionaries rather then arrays

I'm trying to serialize foreign keys as dictionaries instead of arrays. Right now the json looks the following:

{
"slug": "en",
"children": [{
        "slug": "pants",
        "children": [{
                "slug": "products/:level1",
                "children": [{
                    "slug": ":level2/:level3",
                    "children": []
                }]
            },
            {
                "slug": ":productSlug",
                "children": []
            }
        ]
    },
    {
        "slug": "pullovers",
        "children": []
    }
   ]
}

But I'd like it to use the slugs as keys:

{
"en": {
    "children": {
        "pants": {
            "children": {
                "products/:level1": {
                    "children": {
                        ":level2/:level3": {
                            "children": {}
                        }
                    }
                }
            },
            ":productSlug": {
                "children": {}
            }
        ]
    }
 }
}

Is it possible to do that directly in the serializer or do I have to convert it in an additional step?