Rotate actor in direction Z(Yaw)

Hi,

I have a tree mesh that I want to rotate away from the player when cut. With a look at direction between the tree and the player I get the Z(yaw) direction in which the tree should fall. How can I set up the calculations to make the actor rotate 90 degrees towards that direction? Preferably a way that also works if the actor already has rotation in Z.

Thanks!