python children to parent class communication

i have been learning javascript so far but i'm new to python, and i want to do this:

def Node():
    def __init__(self):
        pass
    def callbacks(self):
        # i want this to change the value of the Tree property a to 2, how?:w
        self.self.a = 2
class Tree():
    def __init__(self):
        self.a = 1
    def printt(self):
        b = Node()
        b.callbacks()
        print(self.a)

a = Tree()
a.printt()

could anyone help or propose a better way to do this or even explain if it's a design pattern ?