No, the word ‘tree’ is not a proper noun; it is a common noun.
A proper noun is a specific name used for an individual person, place, or organization, and it is always capitalized. Examples of proper nouns include ‘John’, ‘New York’, or ‘Microsoft’. On the other hand, ‘tree’ refers to a general type of plant, which makes it a common noun. Common nouns are not capitalized unless they begin a sentence.
To put it simply, a proper noun identifies a unique entity, while a common noun groups similar entities together. Therefore, ‘tree’ falls into the common noun category.