I know about the 2 core units rule... I was just messing.
A treeman is a concentration of points. I mean that if the enemy ignores him, you have half your army watching from the sideline. If he falls, you lost the battle even before it begun! So thats why treeman aren't really good in a 500pts battle. You could field them in 1000pts, but only against specific enemy's!
So back to your list, any idea on who you are going to fight? I would recommend what Sirkently said, but I would leave out the treekin. They are expensive to buy, expensive to field, and they always lose on Combat Resolution! (no banner, outranked, outnumbered... etc) That mean you need to make at least 2 wounds just to get even!!
Ah well its a bit what you want but this would be my list:
Branchwraith 65
Spellsinger 90
Dryads 6x 84
Branchnymph
Dryads 6x 72
Dryads 6x 72
Dryads 6x 72
Great Eagle 50
You have a lot of units that also pack a punch, as well as cause fear. Then you also have march blocking, anti-/ pro- magic and a hero to pump out more attacks

(you can put the wraith in the unit with the nymph for challenge purposes)
