SSRS 2012 Report Parameter and multiple filter code

//Define Parameters as below

   MbooleamParaMtr             as Boolean
   MMultipleSelectionParam as Multiple secection Txt Parameter

// your selection criteria as below

  select field1, field2
  from
           Table1
where
           @MbooleamParaMtr = 1                       or
            field1 In (MMultipleSelectionParam)