As Hunited suggested- The angle in which you created this tree isn't Top-down.
Currently it feels like a 2D Sidescroller Tree with a slight drop-shadow
From a top-down view, you would only be able to see the foliage, since it's from directly above. Take this as an example:
http://ak1.picdn.net/shutterstock/videos/13501061/thumb/1.jpgAlternatively, theres the more popular 3/4 View, which is in my opinion a more appealing perspective. A tree in this perspective, you would be able to see both the Foliage, and a limited amount of the tree trunk itself. Take Zelda as an example:
Hopefully this helped