public class TreeNode {

    public var value: Int
    public var leftNode: TreeNode? = nil
    public var rightNode: TreeNode? = nil

    public init(value: Int) {
        self.value = value
    }
}

public func secondHighestNode(head: TreeNode) -> TreeNode? {
    var prev: TreeNode? = nil
    var current = head

    while (true) {
        if let right = current.rightNode {
            prev = current
            current = right
        }
        else if let left = current.leftNode {
            prev = current
            current = left
        } else {
            return prev
        }
    }
}


//EXAMPLE

let n8 = TreeNode(value: 8)
let n3 = TreeNode(value: 3)
let n10 = TreeNode(value: 10)

n8.leftNode = n3
n8.rightNode = n10

let n14 = TreeNode(value: 14)

n10.rightNode = n14

let n12 = TreeNode(value: 12)

n14.leftNode = n12

let n11 = TreeNode(value: 11)
let n13 = TreeNode(value: 13)

n12.leftNode = n11
n12.rightNode = n13

print("\(secondHighestNode(head: n8)?.value)")