Merging two LinkedLists in Swift

LinkedListMerge.swift

import Foundation

class Node {
    
    var val: Int
    
    var next: Node?
    
    init(val: Int) {
        self.val = val
    }
    
}

class LinkedList {
    
    var root: Node?
    
    func insert(val: Int) {
        if self.root == nil {
            self.root = Node(val: val)
        } else {
            self.insert(node: &self.root!, val: val)
        }
    }
    
    func insert(node: inout Node, val: Int) {
        // if val is greater than node
        if val > node.val {
            if node.next == nil {
                node.next = Node(val: val)
            } else {
                self.insert(node: &node.next!, val: val)
            }
        } else {
            // val is less than node, squeeze in node
            let newNode = Node(val: val)
            
            // replace val
            newNode.next = node
            node = newNode
        }
    }
    
    func merge(list: LinkedList) {
        var listNode = list.root
        
        while listNode != nil {
            self.insert(val: listNode!.val)
            listNode = listNode!.next
        }
    }
    
    func printData() {
        var node = self.root
        
        while node != nil {
            print(node!.val)
            node = node!.next
        }
    }
}

var list = LinkedList()
list.insert(val: 2)
list.insert(val: 4)
list.insert(val: 1)
list.insert(val: 2)
list.insert(val: 0)

var listTwo = LinkedList()
listTwo.insert(val: 3)
listTwo.insert(val: 6)
listTwo.insert(val: 1)
listTwo.insert(val: 0)

list.merge(list: listTwo)
list.printData()