triggers

Afternoon guys, I would be very gratefull if anyone could help me on this
one. I´ve tried looking for examples on it, i know it´s simple, but i can´t
get one, so here goes. I need to create a trigger(after insert), preferebly
in plpgsql, as I have already created the lang using createlang, that, takes
value from 2 columns of the record it´s inserting, and  concatenate together
and insert it into a 3rd column,
for example:

I have a table:

employee

id  | branch | name | uniqueId
---|--------|-------|---------

on insert into employee(id,branch,name) values(1,1543,"iande");

the trigger would get both id and branch valeus and insert on uniqueId
so,

select * from employee;

id  | branch | name | uniqueId
-----------------------------
1  | 1543    | iande | 15431


thanks in advance;

Iandé