from collections import OrderedDict

d = {
    'Benefits': {
        1: {
            'BEN1': {
                'D': [{'description': 'D1'}],
                'C': [{'description': 'C1'}]
            }
        },
        2: {
            'BEN2': {
                'D': [{'description': 'D2'}],
                'C': [{'description': 'C2'}]
            }
        }
    }
}

def sort_dict(d):
    items = [[k, v] for k, v in sorted(d.items(), key=lambda x: x[0])]
    for item in items:
        if isinstance(item[1], dict):
            item[1] = sort_dict(item[1])
    return OrderedDict(items)
    #return dict(items)

print(sort_dict(d))