package main;

import javafx.application.Application;
import javafx.scene.Scene;
import javafx.scene.control.SelectionMode;
import javafx.scene.control.TreeItem;
import javafx.scene.control.TreeView;
import javafx.scene.layout.HBox;
import javafx.scene.layout.VBox;
import javafx.stage.Stage;

public class Main extends Application {

    TreeView tree_view;
    int itemIndex = 0;

    @Override
    public void start(Stage stage) {
        HBox content = new HBox();
        tree_view = new TreeView();
        tree_view.getSelectionModel().setSelectionMode(SelectionMode.MULTIPLE);
        TreeItem<String> tree_model = new TreeItem<String>("Root");
        for (int i = 0; i < 10; i++) {
            TreeItem node = new TreeItem("Data item " + i);
            tree_model.getChildren().add(node);
            for (int j = 0; j < 100; j++) {
                node.getChildren().add(new TreeItem("Sub node " + j));
            }
        }
        tree_view.setRoot(tree_model);
        tree_view.setShowRoot(true);
        //tree_view.setCellFactory(new TextFieldTreeCellFactory<String>());

        content.getChildren().add(tree_view);
        stage.setScene(new Scene(content));
        stage.show();
    }
    public static void main(String[] args) {
        launch(Main.class, args);
    }
}


You can use either HBox or VBox. ( I didn't check other containers )

Try to expand or collapse main window (scene) and at the same time expande or collapse items of the tree.
Example 1, if you expand tree a few times, collapse it to root node, and try to change size of scene = size of treeView control will jump to decrease.
Example 2, after first expanding of root node, size of tree view control is not proper.