queryset = [{'a': 1, 'b': 2, 'c': 3, 'value': 1488}, {'a': 4, 'b': 5, 'c': 6, 'value': 500}]
group_by_objs = ['a', 'b', 'c']

def make_nested_dict(d, l):
    if len(l) == 0:
        return {'date': d['value']}
    else:
        return {d[l[0]]: make_nested_dict(d, l[1:])}


def join_dicts(ds):
    if len(ds) == 0:
        return {}
    else:
        return {**ds[0], **join_dicts(ds[1:])}


def group_queryset(queryset, groups):
    if len(queryset) == 0:
        return []
    else:
        return [make_nested_dict(queryset[0], groups), *group_queryset(queryset[1:], groups)]


result = join_dicts(group_queryset(queryset, group_by_objs))

print(result)