How can I do parent/child in the bootstrap multiselect ?

Question

I am working on MVC 5,

How can I bind a category and sub-category to be shown in the same bootstrap multiselect dropdown ?

Here is the table structure and table name is 'productcategory'.

 

 

View,

<pre><script src="~/Scripts/bootstrap-multiselect.js"></script>
<link href="~/css/bootstrap-multiselect.css" rel="stylesheet" />
<script type="text/javascript">
$(function () {
        $('[id*=DDLProductCate]').multiselect({
            includeSelectAllOption: true, buttonWidth: '213%'
        });
    });
</script>

@Html.DropDownListFor(model => model.ShowAdConfigIDs, ViewData["Products"] as List<SelectListItem>, new { @id = "DDLProductCate", @class = "form-control", @multiple = "multiple" })

 How can I do this, inside the same DropDownList's ViewData["Products"] using C# LINQ query ?