I'm not . I haven't . I didn't . In the tree. Because John was rude to her.
Ellipsis is typically anaphoric, i.e. the antecedent occurs earlier in the text.
2.2 Substitutes Substitutes are function words which lack reference but which indicate the category membership of the antecedent. In this category we find certain pronouns, determiners and adverbs. To determine the reference of such an expression, we have to search the preceding text for a possible antecedent. Thus, these expressions provide more information than the substitute forms presented in section 2.2 above. This was his first mistake.