Out of more than 1,000 products examined, only one met federal standards. The great green Christmas tree debate has reached a confusing crescendo. The National Christmas Tree Assn. says farming real trees is perfectly "eco-friendly." Makers of artificial trees say their plastic plants are kinder to the planet because they're reusable. Who's right? As with many green product claims, it's nearly impossible for a consumer to make the call. The Federal Trade Commission wants greater clarity. In late November, it started reviewing its "Green Guides"