Javafx 2 TreeView - hide root item

I created my own TreeView in JavaFX 2 with this tutorial. However I want to hide my root node.

How it looks like right now:

• Root element
  • Parent 1
    • Child 1
    • Child 2
  • Parent 2
    • Child 1

How it should look:

• Parent 1
  • Child 1
  • Child 2
• Parent 2
  • Child 1

thanks, Muki