EnableExplicit

Procedure SortTreeGadgetItems(Gadget)
  Protected a
  For a=0 To CountGadgetItems(Gadget)-1
    If SendMessage_(GadgetID(Gadget),#TVM_GETNEXTITEM,#TVGN_CHILD,GadgetItemID(Gadget,a))
      SendMessage_(GadgetID(Gadget),#TVM_SORTCHILDREN,0,GadgetItemID(Gadget,a))
    EndIf
  Next
  SendMessage_(GadgetID(Gadget),#TVM_SORTCHILDREN,0,0)
EndProcedure

If OpenWindow(0,0,0,500,250,"Window",#PB_Window_SystemMenu|#PB_Window_ScreenCentered)
  TreeGadget(1,10,10,480,230,0)
  
  AddGadgetItem(1,-1,"n",0,0)
    AddGadgetItem(1,-1,"b",0,1)
    AddGadgetItem(1,-1,"z",0,1)
    AddGadgetItem(1,-1,"a",0,1)
  AddGadgetItem(1,-1,"a",0,0)
  AddGadgetItem(1,-1,"j",0,0)
  AddGadgetItem(1,-1,"v",0,0)
  AddGadgetItem(1,-1,"d",0,0)
  AddGadgetItem(1,-1,"b",0,0)
    AddGadgetItem(1,-1,"g",0,1)
    AddGadgetItem(1,-1,"b",0,1)
    AddGadgetItem(1,-1,"j",0,1)
    AddGadgetItem(1,-1,"d",0,1)
  AddGadgetItem(1,-1,"p",0,0)
  AddGadgetItem(1,-1,"s",0,0)
  
  SortTreeGadgetItems(1)
Repeat : Until WaitWindowEvent() = #PB_Event_CloseWindow
EndIf