Not able to add DataValidation in rubyXL while writing to excel

Multi tool use
Not able to add DataValidation in rubyXL while writing to excel
I am using rubyXL gem to write to excel sheet. I need to add a data validation for a column which has dropdown select i.e (List type).
To implement this, I see in rubyXL class we have data_validation.rb
data_validation.rb
gems data_validation code
which has type to array of values of
ST_DataValidationType = %w{ none whole decimal list date time textLength custom }
From this,I don't find a lead to write a dropdown list in the worksheet.
Could someone guide me to implement this dropdown inside the excel sheet?
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