Grouping

private List<SelectOption<string>> groupedCountries = new()
{
    // North America
    new() { Id = "us", Text = "United States", Group = "North America" },
    new() { Id = "ca", Text = "Canada", Group = "North America" },
    new() { Id = "mx", Text = "Mexico", Group = "North America" },
    
    // Europe
    new() { Id = "uk", Text = "United Kingdom", Group = "Europe" },
    new() { Id = "de", Text = "Germany", Group = "Europe" },
    new() { Id = "fr", Text = "France", Group = "Europe" }
};