python - How to get list of instances of inner/nested class created only at one outer instance

I have following code that defines outer and inner classes. I would like to get the instances of the inner class created under one specific instance of the outer class.

class schema():
    def __init__(self,name):
        self.name=name
    class node():
        nodes=[]
        def __init__(self,name):
            self.name=name
            self.nodes.append(self)
        def __call__(self):
            return(self.name)

When I create two instances of the class schema with two different instances of the inner class node I would like to get only the instances of the inner class associated to one of the outer instance.

a=schema('A')
a1=a.node('A1')
a2=a.node('A2')

b=schema('B')
b1=b.node('B1')
b2=b.node('B2')

print({n() for n in a.node.nodes})

I get:

{'B1', 'A1', 'B2', 'A2'}

But I would like to get:

{'A1', 'A2'}

Thank you.