How to add dynamic multiselect list in drop down. I want dynamic. when I will add some new value in the table then it will come in drop down

form.php file (but my code is static i want dynamic)

$fieldset->addField(
            'billingcycle',
            'multiselect',
            [
                'label' => __('Select Billing Cycle'),
                'title' => __('Select Billing Cycle'),
                'name' => 'billingcycle[]',
                'required' => true,
                // 'values' => $this->_options->getOptionsArray(),
                // // 'class' => 'billing',
                'values' => [
                    ["value" => "Once a day","label" => __("Once a day")],
                    ["value" => "Once a week","label" => __("Once a week")],
                    ["value" => "Once a month","label" => __("Once a month")],
                    ["value" => "Once a year","label" => __("Once a year")],
                ],
            ]

        );