Take a look at the node network and click on the choice to the left side labeled "Objects". You should see your bush listed in the Objects block along with planet and background entries.
Right-click on the rectangle that has the bush name on it and chose "Internal Network".
Now you should see a "Parts shader 01" (unless you changed the name.) Right-click on that shader and chose "Internal Network" again.
Now you should see the individual parts that have shaders. Right-click on one (there's probably one called something like "leaves", but it's whatever the name is that was used in the modeling process. Chose "Settings".
You now should see a panel that has the controls for Color, Specular, etc.
Hope this helps.