Where is the JavaFX lambda expressions error?

Question

Java

The program should display labels each time the button is pressed, but when the button is pressed, the label is displayed, and the next time the button is pressed, an error is displayed, but no text.

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)
            );
        }

MISTAKE

"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 = [email protected][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