$builder->add('is_member_of_fund', 'choice', array(
            'expanded' => true,
            'label'    => 'Is trustee a member of the fund?',
            'choices'  => array(
                '1' => 'Yes',
                '0' => 'No'
            ),
            'attr' => array(
                'child_attr' => array(
                'data-bind' => "checked: {$options['knockoutJsNS']}.isMemberOfFund")
            ),
        ));