diff --git a/Kapitel 13/13.1/webview-hello/src/main/java/de/javafxbuch/MainApp.java b/Kapitel 13/13.1/webview-hello/src/main/java/de/javafxbuch/MainApp.java
index ca606be..62abdb2 100644
--- a/Kapitel 13/13.1/webview-hello/src/main/java/de/javafxbuch/MainApp.java	
+++ b/Kapitel 13/13.1/webview-hello/src/main/java/de/javafxbuch/MainApp.java	
@@ -1,5 +1,7 @@
 package de.javafxbuch;
 
+import java.util.ArrayList;
+
 import javafx.application.Application;
 import javafx.collections.ListChangeListener;
 import javafx.concurrent.Worker.State;
@@ -42,13 +44,12 @@ public void start(Stage primaryStage) {
         MenuItem home = new MenuItem("Home");
         navigateMenu.getItems().addAll(home);
         home.setOnAction(e -> engine.load("http://eppleton.de"));
-        menuBar.getMenus().add(navigateMenu);
         Menu historyMenu = new Menu("History");
         engine.getHistory().getEntries().addListener(
                 (ListChangeListener.Change<? extends Entry> c) -> {
                     c.next();
                     for (Entry e : c.getAddedSubList()) {
-                        for (MenuItem i : historyMenu.getItems()) {
+                        for (MenuItem i : new ArrayList<>(historyMenu.getItems())) {
                             if (i.getId().equals(e.getUrl())) {
                                 historyMenu.getItems().remove(i);
                             }
diff --git a/Kapitel 4/4.2.9/controls-treeview/src/main/java/de/javafxbuch/MainApp.java b/Kapitel 4/4.2.9/controls-treeview/src/main/java/de/javafxbuch/MainApp.java
index 22081fe..af8ae52 100644
--- a/Kapitel 4/4.2.9/controls-treeview/src/main/java/de/javafxbuch/MainApp.java	
+++ b/Kapitel 4/4.2.9/controls-treeview/src/main/java/de/javafxbuch/MainApp.java	
@@ -49,11 +49,10 @@ protected void updateItem(Color item, boolean empty) {
                 .add(new TreeItem<Color>(Color.BLUE));
         StackPane pane = new StackPane(treeView);
         Scene scene = new Scene(pane, 300, 250);
+        scene.getStylesheets().add(getClass().getResource("tree.css").toExternalForm());
 
-        primaryStage.setTitle(
-                "TableView Demo");
+		primaryStage.setTitle("TableView Demo");
         primaryStage.setScene(scene);
-
         primaryStage.show();
     }
 
diff --git a/Kapitel 4/4.2.9/controls-treeview/src/main/resources/de/javafxbuch/tree.css b/Kapitel 4/4.2.9/controls-treeview/src/main/resources/de/javafxbuch/tree.css
new file mode 100644
index 0000000..4ca88e3
--- /dev/null
+++ b/Kapitel 4/4.2.9/controls-treeview/src/main/resources/de/javafxbuch/tree.css	
@@ -0,0 +1,7 @@
+.tree-cell > .tree-disclosure-node > .arrow {
+    -fx-rotate: 0;
+}
+
+.tree-cell:expanded > .tree-disclosure-node > .arrow {
+    -fx-rotate: 90;
+}