A vertex subset \( X \) of a simple graph is called OC-irredundant (respectively CO-irredundant) if for each \( v \in X \), \( N(v) – N[X – \{v\}] \neq \emptyset \) (respectively \( N[v] – N(X – \{v\}) \neq \emptyset \)). Sharp bounds involving order and maximum degree for the minimum cardinality of a maximal OC-irredundant set and a maximal CO-irredundant set of a tree are obtained, and extremal trees are exhibited.