Ruby On Rails & bootstrap_form - dropdown in f.text_field

I want to have dropdown at text_field in Ruby on Rails form.
I wrote the code like that:

<div class="dropdown">
  <%= f.text_field :title, class: "dropdown-toggle", data: {toggle:"dropdown"} %>
  <ul class="dropdown-menu" aria-labelledby="dropdownMenuButton">
      # some dropdown items
  </ul>
</div>

My code doesn't work and I get an error...

Uncaught TypeError: Cannot read property 'setAttribute' of null

In my investigation, the problem seems ....

<div class="dropdown"
  <div class="form-group">
    <input class="form-control dropdown-toggle" data-toggle="dropdown" type="text">
  </div>
  <ul class="dropdown-menu" aria-labelledby="dropdownMenuButton">
    # some dropdown items
  </ul>
</div>

Since I'm using bootstrap form, f.text_field is automatically wrapped by "form-group".
I don't need this wrapper in order to make dropdown work well.

So, the following code will work, but I don't know how to realize it by using f.text_field in bootstrap form.

<div class="dropdown"
  <input class="form-control dropdown-toggle" data-toggle="dropdown" type="text">
  <ul class="dropdown-menu" aria-labelledby="dropdownMenuButton">
    # some dropdown items
  </ul>
</div>

Please tell me how to coexist "f.text_field", "form-group", and bootstrap dropdown.