The adjective form of "tree" is "tree-like" or "treeish." These terms describe something that resembles or has characteristics of a tree. However, "arboreal" is another adjective often used in a broader context to refer to things related to trees.
Tree is and adjective
no
"pond" is a noun. An adjective describes a noun. the pond is shallow...shallow being the adjective and pond being the verb. Any "thing" is a noun.
Arboreal.
No. It is a noun.
tall and green
no
It can be considered an adjective when used to indicate a color (olive skin), or something made from olive tree wood. Olive as a noun can refer to the color, the tree, or the fruit of the olive tree.
Tree is neither an adjective nor an adverb. The word tree is a noun, a singular, common, concrete noun; a word for a large form of plant with a stem of wood; a word for a thing.
This tree is tall, but that is the tallest.
No. Christmas is a proper noun. Its use with other nouns (Christmas dinner, Christmas present, Christmas tree) is as a noun adjunct, not an adjective.
It can be an adjective, for example: John took the lastcookie.Or it can be a verb, for example: The tree will lastthrough the winter.