<label for="form2">Размер</label>
<div class="product-size">
    <div class="btn-group size" role="group" ng-repeat='size in vm.sizes'>
        <button type="button" class="btn btn-primary btn-sm size {{size.active}}" ng-click="vm.sizeClick($index)"> {{size.size}}</button>
    </div>
</div>