By default triggers cannot fire themselves. (recursive triggers disabled) so 2 rows will go in, but the second won't fire the trigger
If you have recursive triggers enabled then the trigger will fire itself to a max recursion of level permitted (I think 32) will throw an error and will roll back the entire transaction, including the initial row that fired the first trigger.
Gail Shaw
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability