Function Syntax Help

I having trouble with correct syntax to get this trigger function to compile. I have tried every combination of removing the ‘;’ characters but the function will not compile. Can someone tell me what I am doing wrong, I am stumped. I will be adding addition when clauses the case statement once I get this simplified version to compile.

I am using 9.3.4, both postgres and psql.

CREATE OR REPLACE FUNCTION sn_dm_b.pm_insert_trigger()
RETURNS TRIGGER AS $$
BEGIN
CASE
WHEN NEW.period = 201001
THEN INSERT INTO sn_dm_b.pm201001 VALUES (NEW.*);
END;
RETURN NULL;
END;
$$ LANGUAGE plpgsql;

ERROR: syntax error at or near ";"
LINE 7: END;