trouble with createContent and JTree

Hello.
Could you please help me - I try to write my first plugin, but I don't understant how I can add some nodes into JTree.
When I use contentFactory.createContent and contentFactory.addContent() my JTree is added correctly but in a new tab of the plugin window.

If I add only the main JPanel, my JTree is added with the default values without the nodes that I have already added o_0.
Please tell me where is my mistake?

The code of my tryings is below =(:

public class Manager implements ToolWindowFactory, TreeSelectionListener {

    private JPanel mainPanel;
    private JPanel managerPanel;
    private JPanel ftpLayer;
    private JComboBox ftpConnections;
    private JButton doExpand;
    private JButton doCollapse;
    private JButton doClose;
    private JButton doRefresh;
    private JTree filesInConnection;
    private JScrollPane filesScroll;
    private JLabel label;


    @Override
    public void createToolWindowContent(Project project, ToolWindow toolWindow) {

        //make nodes - test nodes
        DefaultMutableTreeNode root = new DefaultMutableTreeNode("root");

        DefaultMutableTreeNode lv1 = new DefaultMutableTreeNode("lv1");
        DefaultMutableTreeNode lv12 = new DefaultMutableTreeNode("lv12");
        DefaultMutableTreeNode lv2 = new DefaultMutableTreeNode("lv2");

        root.add(lv1);
        lv1.add(lv12);
        root.add(lv2);

        lv2.add( new DefaultMutableTreeNode("lv21"));
        lv2.add( new DefaultMutableTreeNode("lv22"));
        lv2.add( new DefaultMutableTreeNode("lv23"));

        //make tree
        JTree filesInConnection = new JTree(root);
        filesInConnection.addTreeSelectionListener(this);

        JScrollPane filesScroll = new JScrollPane(filesInConnection);

        //get content factory instance
        ContentFactory contentFactory = ContentFactory.SERVICE.getInstance();

        //create content panel
        Content content = contentFactory.createContent(mainPanel, "", false);
        Content f = contentFactory.createContent(filesInConnection, "", false);

        toolWindow.getContentManager().addContent(content, 0);
        toolWindow.getContentManager().addContent(f, 0);
    }

    public void valueChanged(TreeSelectionEvent arg0) {

    }
}