Database Trigger

I have a table called cust_file (cus_no number(3),cus_name varchar2(100))

and another table called
cust_file1 (cus_no1 number(3),cus_name1 varchar2(100))

there is a developed screen (.fmx) allowed user to insert
data in cust_file

I want to create a trigger on the database level
fire each time the user insert data on cust_file
and make the data inserted on cust_file1 table instead of cust_file

How can I perform this task.