<div class="md-form input-group mb-3">

  <span class="input-group-text md-addon">

    Button

  </span>

  <select class="mdb-select">

    <option value="1">Option 1</option>

    <option value="2">Option 2</option>

    <option value="3">Option 3</option>

    <option value="4">Option 4</option>

    <option value="5">Option 5</option>

  </select>

</div>