Is Tree a common noun or proper noun?

The noun 'tree' is a common noun, a general Word for a type of plant. The noun 'tree' is capitalized only when it is the first Word in a sentence.

A proper noun is the name of a specific person, place, or thing. A proper noun is always capitalized.

Examples of proper nouns for the common noun 'tree' are Tree Street, Columbia SC or Oak Tree Academy, Tyler TX.