Abstract: A tree running tool is provided which has a means for actuating a latch for latching a side valve tree to a wellhead. Also disclosed is a tree running tool having an external axially movable actuator, preferably in the form of a sliding piston sleeve which is capable of exerting great forces. Also disclosed is a tree running tool having an external connector unit for connecting the tree running tool to a side valve tree. The connector unit is preferably mounted to the sliding piston sleeve and is for axially mechanically connecting the tree running tool to a linkage extending upwardly from the side valve tree.