Is trees a regular noun

Yes, a regular noun is a noun that forms the plural by adding an -s or an -es to the end of the Word. The plural form for the noun tree is trees; an -s added to the singular.

An irregular plural is a noun that forms the plural in some other way; some examples are:

• child, children
• man, men
• tooth, teeth
• ox, oxen
• knife, knives
• baby, babies