you already did it ... pile them up and let them rot . They will do so in the end, but it takes much longer than making ordinary compost with veg waste etc.
Make your pile as big as possible and make sure that the leaves are well moistened , then just leave them for 2 -3 years ...sorry about the long wait , but it does take a while. Oak take a long time , as do pine needles . You can speed it up by mixing the leaves in with other organic stuff such as veg waste and grass cuttings and manure , but it must all be kept moist , not wet or dry . This way , just treat as normal compost making . A mix of 50% leaves and 50% other organic stuff would be ok . Mix it all well , pile it up , then after it heats up , a few days if there is plenty of manure in , then shift the pile over onto a spot next to the original pile . This makes it all heat up again . A few days later do the same again , making sure you mix all the outside bits well into the rest .Continue till it doesn't heat up anymore , or until you can see that it has changed from what it was into compost . This will give you usable compost in a few weeks , and it will make you fit too, or give you a heart attack , one of the two !!
You can also make it moist by adding pee.... either collect it , or , as long as your place doesn't back onto something like a school ...horror stories ... just pee on the pile when you need to go . You can water the pee down as well , it will kick start the leaves into action , rotting down in less time than if just left to their own devices .
It is best to contain the leaves in a chicken mesh surrounded area , saves them blowing all over the place in the wind.
hope that helps ..
cheers
Russ