Transaction in chained mode

In a C application I want to run several
insert commands within a chained transaction
(for faster execution).

From time to time there will be an insert command

causing an
ERROR: Cannot insert a duplicate key into a unique index

As a result, the whole transaction is aborted and all
the previous inserts are lost.
Is there any way to preserve the data
except working with "autocommit" ?
What I have in mind particularly is something like
"Do not abort on duplicate key error".

Regards, Christoph