The trees were knit on Susan Bates 14" knitting needles in US size 6 (4mm) with a medium/worsted weight white cotton yarn pulled from my stash (I think it was either Lion Cotton (link: http://cache.lionbrand.com/yarns/kitchen.htm) or Lily Sugar n' Cream.) I was chomping at the bit to try a cabling project, but didn't have a cable needle or even a double-pointed needle. I used a large plastic tapestry needle instead. I wouldn't recommend it.
The pattern I used was an adaptation of the Tree of Life Sweater pattern at the Lion Brand Yarn website. To make the tree design a washcloth (or whatever) I used a garter stitch edging on the sides and alternated garter and stockinette stitch on the top and bottom.
I am toying with including the cloth (and maybe this poem) with a wedding gift for some friends who are getting married in April. For now, it is in limbo.
Edit: I ended up giving the washcloth to my newlywed friends as part of a bath stuff gift basket. They don't use it either, just keep it displayed in the bathroom of their home. I am honored.