#Question 3)

    def affichage(point):
        if point.val==None:
            return None
        elif point.g == None and point.d != None:
            print(point.val)
            print(" /    \ ")
            print(None,point.d.affichage())
        elif point.g != None and point.d == None:
            print(point.val)
            print(" /    \ ")
            print(point.g.affichage(),None)
        elif point.g == None and point.d == None:
            print(point.val)
            print(" /    \ ")
            print(None,None)
        else :
            print(point.val)
            print(" /    \ ")
            print(point.g.affichage(),point.d.affichage())