Assigning a variable to an earlier ListNode variable

I have code that works exactly how I want it to but I don't understand why Python is allowing for ListNode x.next to be changed when a separate ListNode y gets an update to its y.next value. see below code:

    class ListNode:
    def __init__(self, val=0, next=None):
        self.val = val
        self.next = next
        
x = ListNode(1, None)
a = ListNode(2, None)
y = x
b = ListNode(5, None)

x.next = a
y.next = b

print(x.val)          >>>       1
print(x.next.val)     >>>       5        # how is this not 2 ???

This flies in the face of what I thought I knew about assigning multiple variables in Python. This seems to be the opposite of how Python handles multiple variables. Notice how in the below code, changing 'y' doesn't change what 'x' is:

x = 5
y = x

y += 1

print(y)      >>>    6
print(x)      >>>    5