using System;

using System.Linq;

using System.Collections.Generic;

using System.Collections;

public class Program

{

    public static void Main()

    {

        List<dynamic> ttt = new List<dynamic>()

        {

            new { Mode = 1, Com = "1_1" },

            new { Mode = 1, Com = "1_2" },

            new { Mode = 2, Com = "2_1" },

            new { Mode = 2, Com = "2_2" },

            new { Mode = 3, Com = "3_1" },

            new { Mode = 3, Com = "3_2" },

        };

        var grouped = ttt.GroupBy(obj => obj.Mode);

        var list = ItemGroup<object>.ConvertGroupResult(grouped, "Mode {0}");

    }

}

​

public class ItemGroup<TValue> : List<TValue>

{   

    public ItemGroup(IGrouping<object, TValue> baseGroup)

    {

        this.AddRange(baseGroup);

        Key = baseGroup.Key;

    }

    public ItemGroup(IEnumerable<TValue> baseGroup, object key)

    {

        this.AddRange(baseGroup);

        Key = key;

    }

    public static List<ItemGroup<TValue>> ConvertGroupResult(IEnumerable<IGrouping<object, TValue>> res, string defaultFormat = "{0}")

    {

        List<ItemGroup<TValue>> list = new List<ItemGroup<TValue>>();

        foreach(var g in res)

        {

            list.Add(new ItemGroup<TValue>(g) { DisplayNameFormat = defaultFormat });

        }

        return list;

    }

    public object Key { get; set; }

    private string dispName = "";

    public string DisplayName 

    { 

        get => dispName == "" ? String.Format(DisplayNameFormat, Key.ToString()) : dispName; 

        set => dispName = value; 

    }

    public string DisplayNameFormat { get; set; } = "{0}";

}