I think that mkkguru misunderstood or misused word "connection". Can you explain in other words what do you mean by "getting the connection to particular item"?

Just to make things clear:
connect() method only sets the signal and slot in such way, that if signal is emitted then the connected slot is called (with emitted arguments). So if you connect your QTreeWidget itemClicked(QTreeWidgetItem *, int) signal to 4 slots, then clicking on item will emit one signal ONCE but this will call every slot connected to your signal, so all your 4 slots will be called. But you did not notice that there is QTreeWidgetItem* argumet in that signal, which is there to let you know what item was clicked. So in your case there should be one slot connected to this itemClicked() signal, where depending on information retrieved from given QTreeWidgetItem*, you will know that this clicked item is pvc, plc, ioc, etc...