using System;

using System.Linq;

public class Program {

    public static void Main() {

        var sampleData = new [] {

            new SampleObject ("Hello World"),

            new SampleObject ("Hi"),

            new SampleObject ("I'm awesome"),

            new SampleObject ("Nice")

        };

        var groupedData = sampleData.GroupBy(x => x.Name.First(), x => x);

        var listViewItems = groupedData.SelectMany(x => {

            var header = new [] { new ListViewItem(x.Key + "") };

            var items = x.Select(y => new ListViewItem(y.Name));

            return header.Concat(items);

        });

        foreach (var item in listViewItems) {

            Console.WriteLine(item.Contents);   

        }

    }

    public class SampleObject {

        public string Name { get; set; }    

        public SampleObject (string name) {

            Name = name;    

        }

    }

    public class ListViewItem {

        public string Contents { get; set; }

        public ListViewItem (string contents) {

            Contents = contents;    

        }

    }

}