Your insert calls a trigger which in turn inserts into the same table and hence there is a cascade of triggers ...
SQL0724N The activation of trigger "<trigger-name>" would exceed
the maximum level of cascading.
Explanation: Cascading of triggers occurs when a triggered SQL
statement in a trigger would result in another trigger being
activated or when a referential constraint delete rule causes
additional triggers to be activated. The depth of this cascading
is limited to 16.
Note that recursive situations where a trigger includes a
triggered SQL statement that directly or indirectly causes the
same trigger to be activated is a form of cascading that is very
likely to cause this error if there are no conditions to prevent
cascading from exceeding the limit.
The "<trigger-name>" specified is one of the triggers that would
have been activated at the seventeenth level of cascading.
User Response: Start with the triggers that are activated by the
UPDATE, INSERT or DELETE statement that received this error. If
any of these triggers are recursive, ensure that there is some
condition that prevents the trigger from being activated more
than the limit allows. If this is not the cause of the problem,
follow the chain of triggers that are activated to determine the
chain that exceeds the cascading limit.
sqlcode: -724
sqlstate: 54038