OnClick doesn't fire when + clicked

The simple breakdown of the problem is that when I set an onClick event on the tree it only fires when the text is clicked, not when the + is clicked.

dhxTree.attachEvent("OnClick", function(id){alert('test');})

any ideas how I can either get rid of the +/- or, ideally make the onClick fire when those are clicked as well.

Many Thanks,

When the +/- is clicked, onOpenStart and then onOpenEnd events fire. onOpenStart need to return true in order to confirm opening/closing