Straightforward yet intriguing, a winning combination.

Ten times as many boys are named Oak as girls: about 50 boys last year to five girls. Of course, nature names don't have any traditional gender identification the way names like John and Mary do, so Oak works well for all babies. Oakley is the most popular Oak name for babies of all genders.

Likable addition to the list of unisex tree names.

For tree huggers.

Ash is a gender-neutral choice that calls to mind the '80s favorite: Ashley. But view it as a nature name -- as in the tree, not the charred bit of soot in the fireplace -- and it makes a cool choice that fits with today's trends.

Traditionally a masculine name in Wales, Celyn (pronounced with a hard K) is now used for both boys and girls. It could work as an alternative to Holly or an honor to a Kelly or a Caitlyn perhaps.

Derby might be considered a word name or a surname-name. In England, it would be pronounced darby, causing confusion with that similar name.