How to use pattern property in data-label C#

I am trying give shape to excel data label using C#. But I din't know about FillFormat.Pattern.

Can anybody please help me, how to use it and give shape to Excel data label. Your help will be appreciated.

This is what I have done so far.

System.Collections.IEnumerator iEChartSeries = seriesCollection.GetEnumerator();
if(iEChartSeries.MoveNext()){
    var oSeries = (Excel.Series)(iEChartSeries.Current);
    Excel.Points pts = (Excel.Points) oSeries.Points(Type.Missing);
    System.Collections.IEnumerator iPoints = pts.GetEnumerator();
    while(iPoints.MoveNext())
    {
        var pt = (Excel.Point)(iPoints.Current);
        pt.HasDataLabel = true;
        pt.DataLabel.Position = Excel.XlDataLabelPosition.xlLabelPositionAbove;

        pt.DataLabel.Font.Name = "Arial";
        pt.DataLabel.Font.FontStyle = "Bold";
        pt.DataLabel.Font.Size = 8;   
        pt.DataLabel.Text = "N";
        pt.DataLabel.Format.Fill.Patterned = ??;// how to get circle/ triangle/ square shapes
    }
}