//
//  DetailViewController.swift
//  SplitView
//
//  Created by Ben Chatelain on 8/25/15.
//  Copyright © 2015 phatblat. All rights reserved.
//

import UIKit

class DetailViewController: UIViewController {

    // MARK: - UIViewController

    override func viewDidLoad() {
        super.viewDidLoad()
    }

    override func viewDidAppear(animated: Bool) {
        super.viewDidAppear(animated)

        navigationItem.leftItemsSupplementBackButton = true

        let displayModeButton = UIBarButtonItem(title: "Menu", style: .Plain,
            target: splitViewController!.displayModeButtonItem().target,
            action: splitViewController!.displayModeButtonItem().action)

        navigationItem.leftBarButtonItem = displayModeButton
        navigationItem.rightBarButtonItem = displayModeButton
    }

}

//
//  DetailViewController.swift
//  SplitView
//
//  Created by Ben Chatelain on 8/25/15.
//  Copyright © 2015 phatblat. All rights reserved.
//

import UIKit

class DetailViewController: UIViewController {

    // MARK: - UIViewController

    override func viewDidLoad() {
        super.viewDidLoad()
    }

    override func viewDidAppear(animated: Bool) {
        super.viewDidAppear(animated)

        navigationItem.rightBarButtonItem = splitViewController?.displayModeButtonItem()
    }

}

--- 
+++ 
@@ -19,7 +19,14 @@
     override func viewDidAppear(animated: Bool) {
         super.viewDidAppear(animated)
 
-        navigationItem.rightBarButtonItem = splitViewController?.displayModeButtonItem()
+        navigationItem.leftItemsSupplementBackButton = true
+
+        let displayModeButton = UIBarButtonItem(title: "Menu", style: .Plain,
+            target: splitViewController!.displayModeButtonItem().target,
+            action: splitViewController!.displayModeButtonItem().action)
+
+        navigationItem.leftBarButtonItem = displayModeButton
+        navigationItem.rightBarButtonItem = displayModeButton
     }
 
 }
Configure displayModeButton to always be visible

http://stackoverflow.com/questions/25852593/uisplitviewcontroller-displaymodebuttonitem#answer-26197227
