How to make a nice dropdown menu of checkboxes with bootstrap 3.2

I'm trying to create a dropdown menu of checkboxes with bootstrap 3.2

I tried the following :

<div class="dropdown">
    <button class="btn btn-default dropdown-toggle" type="button" id="dropdownMenu2" data-toggle="dropdown">
        Select Fields
        <span class="caret"></span>
    </button>
    <ul class="dropdown-menu" role="menu" aria-labelledby="dropdownMenu2">
        <li >
            <a  tabindex="-1" href="#"  ng-repeat="fieldObj in vm.gridOptions.columnDefs">
                <input type="checkbox" ng-model="fieldObj.visible"> 
            </a>
        </li>
        <li style="list-style-type: none">
            <button ng-click="vm.refreshGrid()">OK</button>
        </li>
    </ul>
</div>

The only problem with this 'solution' is that you can't check the checkboxes - they stay unchecked

What would solve it ?