I know I am missing something obvious but I can't seem to implement ObservableCollection in my class below. IE it won't show up in intellsense. Can someone please let me know what I am missing.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Collections;
using System.Collections.ObjectModel;
using System.Reflection;
using System.ComponentModel;

namespace MyBTOList
{
public class InventoryListBTO : List<InventoryBTO>
{
    /// <summary>
    /// Get all inventory records from local database
    /// </summary>
    /// <returns></returns>
    public static InventoryListBTO GetAllInventoryRecords()
    {
        return GetInventoryListBO(Inventory.GetAllInventoryRecordsDb());
    }
 }

 public class InventoryBTO : INotifyPropertyChanged
 {

 }