JSFiddle - React, Tailwind, and code Playground

HTML

<script src="//ajax.googleapis.com/ajax/libs/jquery/1.10.2/jquery.min.js"></script>
<script src="https://rawgithub.com/ivaynberg/select2/master/select2.js"></script>
<link rel="stylesheet" href="https://rawgithub.com/ivaynberg/select2/master/select2.css">
<link rel="stylesheet" href="http://netdna.bootstrapcdn.com/bootstrap/3.0.0-rc2/css/bootstrap.min.css">
Sem input-group
<div class="form-group ">
    
    <select class="form-control input-sm">
        <option value="1">Nome extensoNome extenso Nome extensoNome extensoNome extensoNome extensoNome extensoNome extensoNome extenso</option>
        
    </select>
</div>

Com input-group
<div class="input-group ">
    
    <span class="input-group-addon">@</span>
    <select class="form-control input-sm">
        <option value="1" selected>Nome extensoNome extenso Nome extensoNome extensoNome extensoNome extensoNome extensoNome extensoNome extenso</option>
        
    </select>
</div>

CSS

body {
  /*  padding: 2em 15em;*/
}

.form-control .select2-choice {
    border: 0;
    border-radius: 2px;
}

.form-control .select2-choice .select2-arrow {
    border-radius: 0 2px 2px 0;   
}

.form-control.select2-container {
    height: auto !important;
    padding: 0px;
}

.form-control.select2-container.select2-dropdown-open {
    border-color: #5897FB;
    border-radius: 3px 3px 0 0;
}

.form-control .select2-container.select2-dropdown-open .select2-choices {
    border-radius: 3px 3px 0 0;
}

.form-control.select2-container .select2-choices {
    border: 0 !important;
    border-radius: 3px;
}

.select2-container .select2-choice > .select2-chosen{
    white-space: normal;
}

JavaScript

$(".form-control").select2();