<div class="btn-group" role="group" aria-label="Button group with nested dropdown">
<button type="button" class="btn btn-secondary">1</button>
<button type="button" class="btn btn-secondary">2</button>
<div class="btn-group" role="group">
<button id="btnGroupDrop1" type="button"
class="btn btn-secondary dropdown-toggle"
data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">
Dropdown
</button>
<div class="dropdown-menu" aria-labelledby="btnGroupDrop1">
<a class="dropdown-item" href="#">Dropdown link</a>
<a class="dropdown-item" href="#">Dropdown link</a>
</div>
</div>
</div>