AddRange ObservableCollection Issue

Question

Hi I'm using this link to implement Fastest Observable Collection Best performance for ObservableCollection.AddRange

ObservableCollection Doesn't support AddRange method, so I get notified for each item added, besides what about INotifyCollectionChanging?

But on Calling AddRange() or ReplaceRange() methods multiple times, the performance gets slow, for example

AddRange() executed first time in 0.5 sec.
AddRange() executed 2nd Time in 1 sec.
AddRange() executed 3rd Time in 2.5 sec.

And it keep taking more time to execute methods even with same data.

For Better understanding, here is a code

For Each serie In SeriesList
serie.SeriesDisplayName = "New Series " +    newSeriesCounter.ToString()

 If newSeriesCounter = 1 Then
 serie.Items(1).Number = 500
 End If

 newSeriesCounter += 1
 Next

 Series.Clear()
 Series.AddRange(SeriesList)