<div class="input-group">
  <div class="input-group-prepend">
    <button type="button" class="btn btn-secondary dropdown-toggle" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">
    Action
    </button>
    <div class="dropdown-menu">
    <a class="dropdown-item" href="#">Action</a>
    <a class="dropdown-item" href="#">Another action</a>
    <a class="dropdown-item" href="#">Something else here</a>
    <div role="separator" class="dropdown-divider"></div>
    <a class="dropdown-item" href="#">Separated link</a>
    </div>
  </div>
  <input type="text" class="form-control" aria-label="Text input with dropdown button">
</div>