If he is expecting his colleague's cooperation in these sensitive matters, he is raking up the wrong tree.
Barking up the wrong tree means making a mistaken or misguided effort or assumption.
barking up the wrong tree
The idiomatic expression barking up the wrong tree means pursuing a mistaken or misguided course of action, which fits the context of the sentence. - Option (A) climbing up the wrong tree is not an idiomatic expression and does not convey the intended meaning. - Option (B) cutting down the wrong tree is incorrect as it's not a recognized idiom in English. - Option (C) planting the wrong tree is also not correct, as it does not fit the idiomatic meaning of pursuing the wrong course. - Option (D) barking up the wrong tree is the correct idiom meaning to pursue something incorrectly, making it the right choice.