Bryce has a very limited modeling engine. It can do almost anything if you are patient.
For example, you can import a mesh (3ds, LWO, OBJ etc), and use booleans (postive and negative spaces) to delete part of it. For example, my Hummer avenger is more then 1/2 bryce booleans and roughly an egual part 3d meshes.
I got a Hummer I liked, and deleted part of it via booleans.
Some where (in one of roman legions threads) I posted an image I made entirely of bryce booleans. (a small house on an island, etc).
The strength of Bryce is its simplicity. Most 3d apps are time consuming. Bryce is not.
The other advantage is cost. Bryce costs 1/10th as much as most of them.
Finally there is the superduper way it animates.
The cost is: pisspoor modeler. slow as stink renders. And inability to export 90% of what you make to other 3d apps.
WRT the pyramid.
I can make a pyramid. I can make a copy. I can then delete (via booleans) the lower portions of this pyramid. I can then with change the height, width ratio of the remaining portions.

Here is a sample pyramid. I textured it with this gradiant color so you could more easily see where I cut and where I resized. I made the 1st pyramid, made a copy. Re-sized it. applied a few booleans. I'm not nearly as good as Wyrmshadow (4+yrs of experiance vs. 4 months).. and even so, this took me less then 5minutes.
Parts of everything I have released has included some booleans. Some more then others. It is so simple. Wyrmshadow is constantly scolding me for over thinking things and makeing Bryce far harder then it is.