Do you know how many levels you will have? It would be best to do this through a SQL view. though in crystal the basics is
add the table 4 times,
Link
Table1.ParentID to Table2.ConnectionID
Table2.ParentID to Table3.ConnectionID
Table3.ParentID to Table4.ConnectionID
you want these as right outer joins.
Just remember of you start apply filters to fields in a higher level then what data exists for then you will loose records.