Display node form fieldset using Form State API

<?php
/**
* Display group group_name if control field field_control_name has value 2
*/
function ji_custom_field_group_build_pre_render_alter(&$element) {
  if(isset($element['group_name'])){
    $element['group_name']['#states'] = array(
      'visible' => array(
        ':input[name="field_control_name[und]"]' => array('value' => 2),
      ),
    );
  }
}
?>