public class ViewModel
{
    public ManageComparatorSelectionsViewModel ManageComparatorSelectionsViewModel { get; set; }
    public ManageComparatorItemViewModel CurrentComparatorItem { get; set; }
}


public class ManageComparatorSelectionsViewModel
{
    public IList<Edition> Editions { get; set; }
    public IList<Year> Years { get; set; }
}

public class ManageComparatorItemViewModel
{
    public Edition ChosenEdition { get; set; }
    public Year ChosenYear { get; set; }
}

var mapping = {
        'ManageComparatorSelectionsViewModel.Editions': {
            key: function (data) {
                return ko.utils.unwrapObservable(data.Id);
            }
        },
        'ManageComparatorSelectionsViewModel.Years': {
            key: function (data) {
                return ko.utils.unwrapObservable(data.Id);
            }
        }
    };
    var viewModel = ko.mapping.fromJS(viewModelData, mapping);

    ko.applyBindings(viewModel);

<select data-bind=" template : { 'name' : 'templateID', foreach : optionlist } "></select>

<script type="html/text" id="templateID">
      <option value="${ key }">${ text }</option>
</script>