Example Depot

// Create tree
JTree tree = new JTree();
DefaultTreeModel model = (DefaultTreeModel)tree.getModel();

// Find node to which new node is to be added
int startRow = 0;
String prefix = "J";
TreePath path = tree.getNextMatch(prefix, startRow, Position.Bias.Forward);
MutableTreeNode node = (MutableTreeNode)path.getLastPathComponent();

// Create new node
MutableTreeNode newNode = new DefaultMutableTreeNode("green");

// Insert new node as last child of node
model.insertNodeInto(newNode, node, node.getChildCount());