You have got the concept that you are inserting a row with a reference to a previous row; the very 1st row cannot refer to other rows, so it either must refer to itself, or to nothing.
For the 1st row use "null" for superssn or use its own value.
If you have designed your table that it not only contains the employee's name but also their supervisor's id, then you are designing a "tree" inside the table (

) and you ought to have a separate supervisor table.
[ September 09, 2008: Message edited by: Campbell Ritchie ]