common fig vs fig tree

common fig and fig tree both are nouns.

Word	Noun	Adjective	Verb	Adverb
common fig	Yes	No	No	No
fig tree	Yes	No	No	No

As nouns, fig tree is a hypernym of common fig; that is, fig tree is a word with a broader meaning than common fig:

common fig: Mediterranean tree widely cultivated for its edible fruit
fig tree: any moraceous tree of the tropical genus Ficus; produces a closed pear-shaped receptacle that becomes fleshy and edible when mature

common fig (noun)	fig tree (noun)
Mediterranean tree widely cultivated for its edible fruit	any moraceous tree of the tropical genus Ficus; produces a closed pear-shaped receptacle that becomes fleshy and edible when mature