# Unsure about parse tree of PCFG

I'm new to build parse trees and I'm really unsure if I'm doing this right. So I have this example Grammar (S->Sa, S->aSa, S->a) and the word I'm parsing is simply aaaa.

My solution would look like

Is this right and is this the only possible parse tree?

Your tree is correct. However, it's not the only possible one. Your tree came from the derivation $$S\Rightarrow Sa\Rightarrow aSaa\Rightarrow aaaa$$ a different one would be from $$S\Rightarrow aSa\Rightarrow aSaa\Rightarrow aaaa$$