The chain is obvious, just needs to be strong enough, long enough and terminate with a chainhook on the working end and be secured to your drawbar on the other. The lever part is simple and can be done in a number of ways. Perhaps the simpliest (though not most convenient) is to use a section from a large log, say two feet in diameter by three feet long and place it next to the tree to be removed lying down. The chain is then wrapped securely two or three times tightly around the tree to be removed, then led over the log to your tractor drawbar (drawbar please, not 3PT or anything attached to the 3PT or the safety police will get you). You then just pull with the tractor. The log effectively changes the direction of the force from horizontal to more vertical and therefore pops the tree out of the ground. Roots and tree structure resist lateral forces (wind or straight pulling with the tractor) better than vertical forces (falling up to the sky) so it makes it easier to get the tree or stump out.
Other devices can be substituted for the tree section. A sturdy metal frame built like an "X" will work fine if strong enough and if the feet have pads to keep it from slipping and digging into the soil. Check out this thread:
http://www.tractorbynet.com/forums/build-yourself/129506-tree-puller-hard-get-trees.html Something like that would be great for you as you don't have a FEL bucket to carry around the log.
If you do use the tree section as the pivot point you can just carry it around with you in the tractor's bucket with the chain as you move from tree to tree.