OK, so I'm pretty sure that "orange tree" is considered one subject. If I'm diagramming a sentence it would go on the left as "orange tree."
However, what about "Anjou pears" or "green pears" or French toast?
Would I diagram the following on the left of the vertical line?
"Anjou pears" as one subject instead of Anjou being a proper adjective?
"French toast" as one subject instead of French being a proper adjective?