If you saw a "Tree" then you didn't see a true cranberry. The link has photos of true cranberry plants (Vaccinium macrocarpon). I have them growing in my bog they are a groundcover vine and very small. These are the cranberries most everyone eats at the holidays, in fact I'll be picking cranberries this week in my bog!

If you saw a Cranberry tree (or bush) probably what you saw was Highbush Cranberry which is actually a Virburnum (V. opulus). there are 2 subspecies of this an American and a European (which has taken over much of N. America). The American subspecies has somewhat edible fruit, especially for jams or jellies. the European subspecies is vile tasting and extremely astringent.

Here is a link that might be useful: Cranberry photos