Fixed Vertical branch spawn unpredictability

Turns out all it needed was a little linking for the sake of order :D

Before:
![trees-fix-before](https://f.cloud.github.com/assets/1635159/832077/5bbb2028-f22e-11e2-9c5f-ddc66ebfee5c.jpg)
After:
![trees-fix-after](https://f.cloud.github.com/assets/1635159/832076/587ca332-f22e-11e2-987a-1bb33d5236cc.jpg)