def addtab():
    w = nuke.thisNode()
   # w = nuke.selectedNode()
    w_tab = nuke.Tab_Knob('test', 'test')
    btn = nuke.PyScript_Knob('Clickme', 'Batch Renamer')

    if w.Class() == "Read":
        w.addKnob(w_tab)
        w.addKnob(btn)
        w['Clickme'].setCommand("batchrenamer.main()")
nuke.addOnUserCreate(addtab)