<select class="selectpicker" multiple data-live-search="true" data-live-search-placeholder="Search" data-actions-box="true">
              <option>option1</option>
              <option>option2</option>
              <option>option3</option>
              <option>option4</option>
            </optgroup>
            <optgroup label="filter2">
              <option>option1</option>
              <option>option2</option>
              <option>option3</option>
              <option>option4</option>
            </optgroup>
            <optgroup label="filter3">
              <option>option1</option>
              <option>option2</option>
              <option>option3</option>
              <option>option4</option>
            </optgroup>
</select>

$('.selectpicker').selectpicker(
  {  
    liveSearchPlaceholder: 'Placeholder text'
  }
);

External CSS

  1. https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/css/bootstrap.min.css
  2. https://cdnjs.cloudflare.com/ajax/libs/bootstrap-select/1.12.2/css/bootstrap-select.min.css

External JavaScript

  1. https://code.jquery.com/jquery-1.12.4.min.js
  2. https://cdnjs.cloudflare.com/ajax/libs/bootstrap-select/1.12.2/js/bootstrap-select.min.js
  3. https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/js/bootstrap.min.js