Need check all option in multi selection spinner

I am using this multiselection spinner class in my project .

https://github.com/GunaseelanArumaikkannu/MultiSpinner/blob/master/libmultispinner/src/main/java/com/guna/libmultispinner/MultiSelectionSpinner.java

I need an option of check all as the first item in my spinner.When I check the checkall option, all items in my spinner should get selected. Please provide your take on how to do this