(self)
Should return a structure like:
            [{
                'val': <value>,
                'text': <text>,
                'next': [
                        {
                            'val': <value>,
                            'text' <text>,
                            'next': [...]
                        },
                        {...}
                    ]
            },
            {...}
            ]
Should return a structure like:
            [{
                'val': <value>,
                'text': <text>,
                'next': [
                        {
                            'val': <value>,
                            'text' <text>,
                            'next': [...]
                        },
                        {...}
                    ]
            },
            {...}
            ]
Should return a structure like : [ { val : <value > text : <text > next : [ { val : <value > text <text > next : [ ... ] } { ... } ] } { ... } ]
def drilldown_map(self):
        """
            Should return a structure like:
            [{
                'val': <value>,
                'text': <text>,
                'next': [
                        {
                            'val': <value>,
                            'text' <text>,
                            'next': [...]
                        },
                        {...}
                    ]
            },
            {...}
            ]
        """
        raise NotImplementedError("drilldown_map must be implemented")
def drilldown_map ( self ) : raise NotImplementedError ( "drilldown_map must be implemented" )