We will make two tables and an union view for them. Then we will create a trigger which inserts a new record in one of the tables according to values.

First lets create the tables and the view.

create table first_table(
  id integer not null primary key,
  txt varchar
);

create table second_table(
  id integer not null primary key,
  txt varchar
);

create view all_tables (id,from_table,txt)
as select id,'first',txt from first_table
union all
select id,'second',txt from second_table;

Now lets create a trigger instead of insert for the view and insert some data.

create trigger insert_all_tables
  instead of insert on all_tables referencing new as N{
    if(N.from_table = 'first' or N.from_table = 'all')
      insert into first_table (id,txt) values(N.id,N.txt);

    if(N.from_table = 'second' or N.from_table = 'all')
      insert into second_table (id,txt) values(N.id,N.txt);
  };

  insert into all_tables (id,from_table,txt) values (1,'first','into first');
  insert into all_tables (id,from_table,txt) values (2,'second','into second');
  insert into all_tables (id,from_table,txt) values (3,'all','into all');

  select * from all_tables;

  id       from_table  txt
  INTEGER  VARCHAR  VARCHAR
  _______________________________________________________________________________

  1        first    into first
  3        first    into all
  2        second   into second
  3        second   into all