、。
I wanted to learn more about trees as well.
Literal
Tree [about-についても], more know-want [quotative-と] thought.
~について ('about, concerning, regarding') is the standard particle for topic-about-which. Adding も ('also') turns it into ~についても, 'also about X,' implying the speaker wants to learn about trees in addition to whatever else was being discussed. ~たい attached to 知る and embedded under と思う gives a softened statement of wish.