You can add INSERT and UPDATE in the same create statement separated by a comma. Something like below
For more info on Create TRIGGER refer : http://msdn.microsoft.com/en-us/library/ms189799.aspx
CREATE TRIGGER [dbo].[triggername] ON [dbo].[tablename] AFTER INSERT, UPDATE
AS
BEGIN
IF EXISTS(SELECT * FROM DELETED)
BEGIN
SELECT * FROM DELETED;
END
ELSE
BEGIN
INSERT INTO tablename_history;
SELECT * FROM INSERTED;
END
PRINT 'AFTER INSERT/UPDATE Trigger fired.';
END