Assign callback for a left mouse click on a tree widget

The demo code in axlform.il shows how to capture a right mouse button click for a popup for a tree.

I'm not quite sure how to simply catch a left mouse click event to run a callback to load some other field's values.
I don't actually want it to pop up anything either.  Just run another SKILL procedure.

Any hints?

Below is what I'm using in a case statement for my RMB popups.  What would be different
for the left and no popup?

("tree"
when( checkForm->event == 'rightpopup
axlUIWPrint(nil "Mike: Trying to adjust the rightpopups...")
case(checkForm->curValue
("run_task" axlUIWPrint(nil "Running Task."))
("view_hyperlinks" axlUIWPrint(nil "Viewing Hyperlinks..."))
);End case.
);End when.
);End tree.


Regards!

-Mike