private async void btnParallel_Click(object sender, RoutedEventArgs e)
        {
            try
            {
                tbResult.Text    = "";
                pbDownload.Value = 0;

                // Create an insatnce of Progress Oject
                Progress <ProgressReportModel> progress = new Progress <ProgressReportModel>();
                ParallelOptions parallelOptions         = new ParallelOptions()
                {
                    CancellationToken = cancellationTokenSource.Token
                };

                // Wire up Progress Change Event
                progress.ProgressChanged += Progress_ProgressChanged;

                try
                {
                    // Start the Job for Download Website Content and Pass as parameter of progress and cancellation Token Object
                    await websiteContext?.RunDownloadParallelAsync(progress, parallelOptions);
                }
                catch (Exception ex) when(ex is OperationCanceledException || ex is TaskCanceledException)
                {
                    tbResult.Text += $"The async download was cancelled. { Environment.NewLine }";
                }
                finally
                {
                    // if cancellation request true then dispose cancelllation Token
                    if (cancellationTokenSource.IsCancellationRequested == true)
                    {
                        cancellationTokenSource.Dispose();
                        cancellationTokenSource = new CancellationTokenSource();
                    }
                }
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message);
            }
        }