Nav widget - Classname for UL at level 1

I’m looking for the settings to give a class name to the ul at level 1 in the Nav widget.


           [

                'label' => '<i class="fa fa-credit-card"></i> <span class="nav-label">Financieel</span></span>',

                'items' => [

                    [

                        'label' => 'Saldo',

                        'url' => ['/']

                    ],

                    [

                        'label' => 'Facturen',

                        'url' => ['/']

                    ],

                    [

                        'label' => 'Aandachtspunten',

                        'url' => ['/']

                    ]

                ]

            ],

I’ve tried so many things, and I don’t believe a jquery call is the only option