Hope this helps

//Category you are looking for
string categoryName = "The category you want to look for";

//Having that you have everithing under home node  
var home = Model.Content.AncestorOrSelf(1);

//Select the category node using the category name
var category = home.Descendants("category").Where(c => c.GetPropertyValue<string>("name") == categoryName).ToList();

if(category != null && category.Count > 0)
{
    //Having that northernground.ucontentdropdown store the nodeId and it does as string
    string categoryId = category.First().Id.ToString();

    //Get all the products and filter them by the selected category
    return home.Descendants("productsDetails").Where(p => p.GetPropertyValue<string>("category") == categoryId).ToList();
}

return null;

is working on a reply...