// Initialize
DefaultMutableTreeNode root = new DefaultMutableTreeNode("Root");
JTree tree = new JTree(root);

// Change
DefaultMutableTreeNode node = new DefaultMutableTreeNode("New");
root.add(node);

// Update
TreeModel treeModel = tree.getModel();
treeModel.reload();
tree.scrollPathToVisible(new TreePath(node.getPath()));
tree.setSelectionPath(new TreePath(categoryNode.getPath()));