Can you make this class as SortedDict like .NET?
1. add new item in sorted order.
2. For the duplicated items, they can be add either behind or ahead. (C#'s SortedDict can use "Call back" to do so).
For example:
Raw Items: item0,item1,item2,item9,item4,item0
Result: item0,item0(last addition),item1,item2,item4,item9 -Sorted Ascending and appending the same item
item0(last addition),item0,item1,item2,item4,item9 -Sorted Ascending and inserting the same item

Such feature is useful for multi-column sorting.