Hi,
I have a question for you, did you delete the default height-field terrain and then go Add Terrain > Power Fractal the terrain will not show up as the Power Fractal is not connected to the Compute Train Node which is why it is not showing up.
Two solutions.
1. Create your Power Fractal First before deleting the Height Field node, this way your Power fractal will show up in you node tree.
2. After deleting the height field node go to the Terrain Group and go create the Power-Fractal via Create Shader > Displacement Shader > Power-Fractal, then connect the Power Fractal to the Compute Terrain Node and it will show up in you node tree.
Regards to you.
Cyber-Angel