def optionMenuCallback(*args):
    fn = cmds.menuItem (args[0], q=True, c=True)
    if fn:
        fn()

def menu1Callback():
    startAnimation = cmds.playbackOptions(query=True, minTime=True)
    endAnimation = cmds.playbackOptions(query=True, maxTime=True)

def menu2Callback():
    startAnimation = cmds.findKeyframe(which='first')
    endAnimation = cmds.findKeyframe(which='last')

w = cmds.window(w=150, h=100)
cmds.columnLayout(adjustableColumn=True)
form = cmds.formLayout(numberOfDivisions=100)
exportSelection = cmds.optionMenuGrp(label='example', cc=optionMenuCallback)
menuItem1 = cmds.menuItem('item1', c = menu1Callback)
menuItem2 = cmds.menuItem('item2', c= menu2Callback)
okayBtn = cmds.button(label='okay!', command=self.buttonPressed, width=150, height=35)
cmds.formLayout(form, edit=True, attachForm=[\
(exportSelection, 'top', 18),\
(exportSelection, 'left', 45),\
(okayBtn, 'left', 70),\
(okayBtn, 'top', 90)])
cmds.showWindow(w)