如何使用bootstrap multiselect显示最后的全选选项？

<link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/bootstrap@5.3.0/dist/css/bootstrap.min.css">
<link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/bootstrap-multiselect@0.9.16/dist/css/bootstrap-multiselect.min.css">
<script src="https://cdn.jsdelivr.net/npm/bootstrap@5.3.0/dist/js/bootstrap.bundle.min.js"></script>
<script src="https://cdn.jsdelivr.net/npm/bootstrap-multiselect@0.9.16/dist/js/bootstrap-multiselect.min.js"></script>

<select id="mySelect" multiple="multiple">
  <option value="option1">选项1</option>
  <option value="option2">选项2</option>
  <option value="option3">选项3</option>
  <!-- 其他选项 -->
</select>

$(document).ready(function() {
  $('#mySelect').multiselect();
});

<select id="mySelect" multiple="multiple">
  <optgroup label="全选">
    <option value="all">全选</option>
  </optgroup>
  <optgroup label="其他选项">
    <option value="option1">选项1</option>
    <option value="option2">选项2</option>
    <option value="option3">选项3</option>
    <!-- 其他选项 -->
  </optgroup>
</select>

$(document).ready(function() {
  $('#mySelect').multiselect({
    onChange: function(option, checked) {
      if ($(option).val() === 'all') {
        if (checked) {
          $('#mySelect option').prop('selected', true);
        } else {
          $('#mySelect option').prop('selected', false);
        }
      }
    }
  });
});