BinaryTree.swift

class BinaryTree<T: Comparable & CustomStringConvertible> {
    
    private var rootNode: TreeNode<T>?
    
    func insert(element: T) {
        let node = TreeNode(data: element)
        if let rootNode = self.rootNode {
            self.insert(rootNode, node)
        } else {
            self.rootNode = node
        }
    }
    
    // RECURSIVE FUNCTION
    private func insert(_ rootNode: TreeNode<T>, _ node: TreeNode<T>) {
        if rootNode.data > node.data {
            if let leftNode = rootNode.leftNode {
                self.insert(leftNode, node)
            } else {
                rootNode.leftNode = node
            }
        } else {
            if let rightNode = rootNode.rightNode {
                self.insert(rightNode, node)
            } else {
                rootNode.rightNode = node
            }
        }
    }
}