调用下面的方法:
/**
* Invoked this to insert newChild at location index in parents children.
* This will then message nodesWereInserted to create the appropriate
* event. This is the preferred way to add children as it will create
* the appropriate event.
*/
public void insertNodeInto(MutableTreeNode newChild,
MutableTreeNode parent, int index){
parent.insert(newChild, index);