Now this is the DIY method, cut the bottom of a liter bottle of a soda pop, turn it upside down into a hole next to the plant and water into the base of the bottle a slow drip, is that simple enough?
I usually plant a 2inch diameter pipe that is as long as the root ball along side the tree and put a slow dripping hose in the pipe, this takes the water down to the root system, trees need about 3 years to establish.