Sycamore tree is a noun. It is not capitalised.
The word tree is a singular noun. The plural would be trees.
"Deciduous" is an adjective. It describes trees that shed their leaves annually.
It's a noun.
Boulevard is a noun. It refers to a wide street in a city or town, often lined with trees or buildings.
part of speech
The part of speech for this particular word is a noun.
The part of speech for "answer" is a noun.
adverb
what part of speech is beneath
s
The part of speech for "explicit" is an adjective.
The part of speech for "twirl" is a verb.