Ok here it goes… my first attempt at helping someone with Bryce 
Here is how I made this image.
1. I created a new scene and created a cube from the “Create” option
2. I stretched the cube on the Z Axis
3. While the Cube was still selected, I used CTRL-D to make a duplicate
4. I stretched this second copy on the Z and X Axis it is important to stretch it quite longer on the Z Axis as you will be tilting this one
and the X Axis a bit wider so as to make sure to cut properly.
5. From the edit menu I tilted the duplicate and stretched copy on the X Axis. Viewing from the TOP and RIGHT video to make sure it was aligned up properly.
6. Select the original rectangle should be “Cube1” click on the “A” next to the object to enter the “Object Attributes” screen and set it to “Positive”
7. Next do the same for the duplicated object “Cube2” and this time set it to “Negative” .
8 Select both objects Cube1 & Cube2 and group both objects.
Now when you render the scene it should look like the object I’ve created, I rushed the one I made it, so its not as perfect as it could be if you look at the pointed edge.
I hope this helps.
Click thumbnail to see full-size image