mapkey act ~ RButtonArm `main_dlg_cur` `PHTLeft.AssyTree` `node69`;\
mapkey(continued) ~ PopupOver `main_dlg_cur` `ActionMenu`1 `PHTLeft.AssyTree`;\
mapkey(continued) ~ Open `main_dlg_cur` `ActionMenu`;~ Close `main_dlg_cur` `ActionMenu`;\
mapkey(continued) ~ Activate `main_dlg_cur` `MakeActive`;
This seems to work in WF5. Pick an item on the tree and use the mapkey to activate it.
I recorded it by first selecting an item, then starting the mapkey recorder, right clicked next to some datum planes to get Activate without activating a different part, and then stopped the recording.