JTree Animated GIF example http://ateraimemo.com/Swing/AnimatedIconInTableCell.html

AnimatedTreeNodeTest.java

import java.awt.*;
import java.awt.image.ImageObserver;
import java.util.Objects;
import javax.swing.*;
import javax.swing.tree.*;

public class AnimatedTreeNodeTest {
  public JComponent makeUI() {
    ImageIcon icon = new ImageIcon(getClass().getResource(
        "restore_to_background_color.gif"));

    DefaultMutableTreeNode root = new DefaultMutableTreeNode("root");
    DefaultMutableTreeNode s0 = new DefaultMutableTreeNode(new NodeObject("a"));
    DefaultMutableTreeNode s1 = new DefaultMutableTreeNode(new NodeObject("b", icon));
    root.add(s0);
    root.add(s1);
    JTree tree = new JTree(new DefaultTreeModel(root));
    tree.setCellRenderer(new DefaultTreeCellRenderer() {
      @Override public Component getTreeCellRendererComponent(
          JTree tree, Object value, boolean selected, boolean expanded, boolean leaf,
          int row, boolean hasFocus) {
        JLabel l = (JLabel) super.getTreeCellRendererComponent(
            tree, value, selected, expanded, leaf, row, hasFocus);
        if (value instanceof MutableTreeNode
            && ((DefaultMutableTreeNode) value).getUserObject() instanceof NodeObject) {
          NodeObject uo = (NodeObject) ((DefaultMutableTreeNode) value).getUserObject();
          l.setText(Objects.toString(uo.title, ""));
          l.setIcon(uo.icon);
        } else {
          l.setText(Objects.toString(value, ""));
          l.setIcon(null);
        }
        return l;
      }
    });
    TreePath path = new TreePath(s1.getPath());
    //Wastefulness: icon.setImageObserver((ImageObserver) tree);
    icon.setImageObserver(new ImageObserver() {
      @Override public boolean imageUpdate(
          Image img, int infoflags, int x, int y, int w, int h) {
        if (!tree.isShowing()) {
          return false;
        }
        Rectangle cellRect = tree.getPathBounds(path);
        if ((infoflags & (FRAMEBITS | ALLBITS)) != 0 && Objects.nonNull(cellRect)) {
          tree.repaint(cellRect);
        }
        return (infoflags & (ALLBITS | ABORT)) == 0;
      }
    });
    return new JScrollPane(tree);
  }
  public static void main(String... args) {
    EventQueue.invokeLater(() -> {
      JFrame f = new JFrame();
      f.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
      f.getContentPane().add(new AnimatedTreeNodeTest().makeUI());
      f.setSize(320, 240);
      f.setLocationRelativeTo(null);
      f.setVisible(true);
    });
  }
}

class NodeObject {
  public final Icon icon;
  public final String title;
  protected NodeObject(String title) {
    this(title, null);
  }
  protected NodeObject(String title, Icon icon) {
    this.title = title;
    this.icon = icon;
  }
}