如何在Yii2的下拉列表中添加额外选项

I have a dropdown list in my yii2 application which fetches data from database table. now i want to add an extra options to my dropdownlist with value=1 and display=admin

my current dropdown list is :

<?= Html::dropDownLIst('assign_to', null, 
                    ArrayHelper::map(PhCrmUser::findAll(['user_type' => 'executive_manager', 'status' => CrmUser::STATUS_ACTIVE]), 'id',
                       function($model, $defaultValue) {
                          return $model['first_name']." ".$model['last_name'];
                       }
                     ),
                    ['class' => 'form-control', 'prompt' => 'Assign to Manager']
                  )?>

it displays output as

<select class="form-control" name="assign_to">
<option value="">Assign to Manager</option>
<option value="8">Matt Demon</option>
<option value="10">Vinit Singh</option>
<option value="14">dsfds sdfsdf</option>
</select>

now i want to add and extra static option to my dropdownlist how to achive it in yii. my output should look like.

<select class="form-control" name="assign_to">
<option value="">Assign to Manager</option>
<option value="1">Admin</option>
<option value="8">Matt Demon</option>
<option value="10">Vinit Singh</option>
<option value="14">dsfds sdfsdf</option>
</select>

Just add it to values array

<?= Html::dropDownLIst('assign_to', null, 
                ['1' => 'Admin'] + ArrayHelper::map(PhCrmUser::findAll(['user_type' => 'executive_manager', 'status' => CrmUser::STATUS_ACTIVE]), 'id',
                   function($model, $defaultValue) {
                      return $model['first_name']." ".$model['last_name'];
                   }
                 ),
                ['class' => 'form-control', 'prompt' => 'Assign to Manager']
              )?>