Mirror Tree [Swift]

Given two binary tree T1 and T2. Write a function to validate if trees are mirror to each other.

Example

T1:                                     T2
        1                                1
   2         3                      3       2
4     5   6     7                7    6   5   4 

For two tree T1 and T2 to be mirror. Their root node key must me same. and the left sub-tree of T1 and right sub-tree of T2 should be mirror and vice versa.

class Node {
    init(item: Int) {
        self.item = item
        left = nil
        right = nil
    }
    var item : Int
    var left: Node?
    var right: Node?
}


func isMirror(head1: Node?, head2: Node?) -> Bool {
    
    if (head1 == nil) && (head2 == nil) {
        return true
    }
    
    
    if (head1 == nil) || (head2 == nil) {
        return false
    }
    
    return (head1?.item == head2?.item) &&
            isMirror(head1: head1?.left, head2: head2?.right) &&
            isMirror(head1: head1?.right, head2: head2?.left)
}
//
var a: Node = Node(item: 1)
a.left = Node(item: 2)
a.right = Node(item: 3)
a.left?.left = Node(item: 4)
a.left?.right = Node(item: 5)

var b: Node = Node(item: 1)
b.left = Node(item: 3)
b.right = Node(item: 2)
b.right?.right = Node(item: 4)
b.right?.left = Node(item: 5)
print(isMirror(head1: a, head2: b))