Sometimes it is grayed out on capable systems. I know, it happened on my Dell/Windows 7. Here's how to fix this.
If you have enough memory for 3D functions, you can repair this. 512 MB vram at least. Most video cards meet that spec.
Open a new blank document.
From the 3D menu, choose "New 3D Extrusion from Selected layer". You will be sent into the 3D workspace.
Then try: Filter menu > Render... and Tree, Flame, and Frame should be active.
Gene