Does anyone know the method to add another MutableTree Node to a tree
after a DefaultMutableTreeNode has been added?  Or how to add another
node to the tree?

I tried to add a 2nd DefaultMutableTreeNode to a tree with add() but
got an error.  My code follows :

     // create node 1 of tree2
     DefaultMutableTreeNode top2 = new
DefaultMutableTreeNode("Node1");
     
     // create subtree of "A"
     DefaultMutableTreeNode aa = new DefaultMutableTreeNode("Sub node
1");
     top2.add(aa);
     DefaultMutableTreeNode aa1 = new DefaultMutableTreeNode("A1");
     aa.add(aa1);
     DefaultMutableTreeNode aa2 = new DefaultMutableTreeNode("A2");
     aa.add(aa2);

     // create subtree of "B"
     DefaultMutableTreeNode ab = new DefaultMutableTreeNode("Sub node
2");
     top2.add(ab);
     DefaultMutableTreeNode ab1 = new DefaultMutableTreeNode("B1");
     ab.add(ab1);
     DefaultMutableTreeNode ab2 = new DefaultMutableTreeNode("B2");
     ab.add(ab2);
     DefaultMutableTreeNode ab3 = new DefaultMutableTreeNode("B3");
     ab.add(ab3);

     // create node 2 of tree2
     DefaultMutableTreeNode top2a = new DefaultMutableTreeNode("Node
2");
     
     // create subtree of "A"
     DefaultMutableTreeNode a2a = new DefaultMutableTreeNode("Sub
node 3");
     top2a.add(a2a);
     DefaultMutableTreeNode a2a1 = new DefaultMutableTreeNode("A1");
     a2a.add(a2a1);
     DefaultMutableTreeNode a2a2 = new DefaultMutableTreeNode("A2");
     a2a.add(a2a2);

     // create subtree of "B"
     DefaultMutableTreeNode a2b = new DefaultMutableTreeNode("Sub
node 4");
     top2a.add(a2b);
     DefaultMutableTreeNode a2b1 = new DefaultMutableTreeNode("B1");
     a2b.add(a2b1);
     DefaultMutableTreeNode a2b2 = new DefaultMutableTreeNode("B2");
     a2b.add(a2b2);
     DefaultMutableTreeNode a2b3 = new DefaultMutableTreeNode("B3");
     a2b.add(a2b3);

     JTree tree2 = new JTree(top2);
     tree2.add(top2a);   // this line gave me the error
                         // cannot resolve symbol add()