Clone Tree

class TreeNode{
    var value : Int
    var subNode : [TreeNode]
    init(_ value: Int) {
        self.value = value
        subNode = [TreeNode]()
    }
}

func cloneTree(_ root : TreeNode?) -> TreeNode?{
    guard let root = root else {
        return nil
    }
    let newNode = TreeNode(root.value)
    for child in root.subNode {
        newNode.subNode.append(cloneTree(child)!)
    }
    return newNode
}