C# Excel Add In programmatically Add In Memory Drop Down with multiple selection on Excel sheet?

Add In Memory Drop Down/Pick list with multiple selection

CellRange range7 = workbook.Worksheets[0].Range["H2:H30"];  
workbook.Worksheets[0].Range["Z"+b].DataValidation.DataRange = range7;

above the code only single selection of drop down list but how to implementation for multiple selection? result will be look like below the image