Dynamically Set The Option Values?

I have 2 different lists: EmployeeNames and Names. I read the values in Names and that of EmployeeNames.

If EmployeeNames exists in Names, I must not add that value to "ToSelectBox" but to "FromSelectBox".

If EmployeeNames doesn`t exist in Names, I must add that value to "ToSelectBox" but not to "FromSelectBox".

How can I do that dynamically?

I have 2 option values as follows:

<select id="fromSelectBox" multiple="multiple" >
<% foreach (var item in Model.EmployeeNames) { %>
<option value="<%=Html.Encode(Item.Text)%>"><%=Html.Encode(item.Text)%></option>
<%}
%>
</select>
select id="ToSelectBox" multiple="multiple" >
<% foreach (var item in Model.Names) { %>
<option value="<%=Html.Encode(Item.Text)%>"><%=Html.Encode(item.Text)%></option>
<%}
%>
</select>