Где ошибка JavaFX lambda expressions?

Random rand = new Random();
        for (int i = 0; i < 100; i++) {
            Button btn = new Button("APPEAR A TEXT");
            root.getChildren().add(btn);
            int x = rand.nextInt((int) scene.getWidth());
            int y = rand.nextInt((int) scene.getHeight());
            Text text = new Text(x,y,"TEXT");
            btn.setOnAction(
                    event ->
                            root.getChildren().add(text)
            );
        }

"C:\Program Files\Java\jdk1.8.0_73\bin\java" -Didea.launcher.port=7538 "-Didea.launcher.bin.path=D:\Program Files (x86)\JetBrains\IntelliJ IDEA Community Edition 2016.1.3\bin" -Dfile.encoding=UTF-8 -classpath "C:\Program Files\Java\jdk1.8.0_73\jre\lib\charsets.jar;C:\Program Files\Java\jdk1.8.0_73\jre\lib\deploy.jar;C:\Program Files\Java\jdk1.8.0_73\jre\lib\ext\access-bridge-64.jar;C:\Program Files\Java\jdk1.8.0_73\jre\lib\ext\cldrdata.jar;C:\Program Files\Java\jdk1.8.0_73\jre\lib\ext\dnsns.jar;C:\Program Files\Java\jdk1.8.0_73\jre\lib\ext\jaccess.jar;C:\Program Files\Java\jdk1.8.0_73\jre\lib\ext\jfxrt.jar;C:\Program Files\Java\jdk1.8.0_73\jre\lib\ext\localedata.jar;C:\Program Files\Java\jdk1.8.0_73\jre\lib\ext\nashorn.jar;C:\Program Files\Java\jdk1.8.0_73\jre\lib\ext\sunec.jar;C:\Program Files\Java\jdk1.8.0_73\jre\lib\ext\sunjce_provider.jar;C:\Program Files\Java\jdk1.8.0_73\jre\lib\ext\sunmscapi.jar;C:\Program Files\Java\jdk1.8.0_73\jre\lib\ext\sunpkcs11.jar;C:\Program Files\Java\jdk1.8.0_73\jre\lib\ext\zipfs.jar;C:\Program Files\Java\jdk1.8.0_73\jre\lib\javaws.jar;C:\Program Files\Java\jdk1.8.0_73\jre\lib\jce.jar;C:\Program Files\Java\jdk1.8.0_73\jre\lib\jfr.jar;C:\Program Files\Java\jdk1.8.0_73\jre\lib\jfxswt.jar;C:\Program Files\Java\jdk1.8.0_73\jre\lib\jsse.jar;C:\Program Files\Java\jdk1.8.0_73\jre\lib\management-agent.jar;C:\Program Files\Java\jdk1.8.0_73\jre\lib\plugin.jar;C:\Program Files\Java\jdk1.8.0_73\jre\lib\resources.jar;C:\Program Files\Java\jdk1.8.0_73\jre\lib\rt.jar;C:\Users\Даниил\IdeaProjects\JavaFX\out\production\JavaFX;D:\Program Files (x86)\JetBrains\IntelliJ IDEA Community Edition 2016.1.3\lib\idea_rt.jar" com.intellij.rt.execution.application.AppMain sample.Main
Exception in thread "JavaFX Application Thread" java.lang.IllegalArgumentException: Children: duplicate children added: parent = Group@4d6d456[styleClass=root]
	at javafx.scene.Parent$2.onProposedChange(Parent.java:454)
	at com.sun.javafx.collections.VetoableListDecorator.add(VetoableListDecorator.java:206)
	at sample.Main.lambda$start$0(Main.java:35)
	at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:86)
	at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238)
	at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
	at com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
	at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
	at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
	at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
	at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
	at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
	at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
	at com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
	at com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:49)
	at javafx.event.Event.fireEvent(Event.java:198)
	at javafx.scene.Node.fireEvent(Node.java:8411)
	at javafx.scene.control.Button.fire(Button.java:185)
	at com.sun.javafx.scene.control.behavior.ButtonBehavior.mouseReleased(ButtonBehavior.java:182)
	at com.sun.javafx.scene.control.skin.BehaviorSkinBase$1.handle(BehaviorSkinBase.java:96)
	at com.sun.javafx.scene.control.skin.BehaviorSkinBase$1.handle(BehaviorSkinBase.java:89)
	at com.sun.javafx.event.CompositeEventHandler$NormalEventHandlerRecord.handleBubblingEvent(CompositeEventHandler.java:218)
	at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:80)
	at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238)
	at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
	at com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
	at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
	at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
	at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
	at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
	at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
	at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
	at com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
	at com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:54)
	at javafx.event.Event.fireEvent(Event.java:198)
	at javafx.scene.Scene$MouseHandler.process(Scene.java:3757)
	at javafx.scene.Scene$MouseHandler.access$1500(Scene.java:3485)
	at javafx.scene.Scene.impl_processMouseEvent(Scene.java:1762)
	at javafx.scene.Scene$ScenePeerListener.mouseEvent(Scene.java:2494)
	at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:352)
	at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:275)
	at java.security.AccessController.doPrivileged(Native Method)
	at com.sun.javafx.tk.quantum.GlassViewEventHandler.lambda$handleMouseEvent$354(GlassViewEventHandler.java:388)
	at com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(QuantumToolkit.java:389)
	at com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:387)
	at com.sun.glass.ui.View.handleMouseEvent(View.java:555)
	at com.sun.glass.ui.View.notifyMouse(View.java:937)
	at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
	at com.sun.glass.ui.win.WinApplication.lambda$null$148(WinApplication.java:191)
	at java.lang.Thread.run(Thread.java:745)

Process finished with exit code 0