C#

Form1 form = new Form1();
form.richTextBox1.Text = "whatever!";

// 1. declare a delegate
public delegate void AddTreeNodeHandler(TreeNode node);
...
// 2. handler for the delegate
void myAddTreeNode(TreeNode node)
{
    treeView.Nodes.Add(node);
}
...
// 3. Start the thread (something like this.)
// Pass any control created by main thread and delegate that will add node.
MyThread t = new MyThread(treeView, new AddTreeNodeHandler(myAddTreeNode));
Thread t = new Thread(new ThreadStart(t.ThreadMain));
t.Start();
...
// 4. Thread class
class MyThread
{
    Control ctl;
    AddTreeNodeHandler atn;
    void MyThread(Control ctl, AddTreeNodeHandler atn)
    {
        this.ctl = ctl;  // Save for later user
        this.atn = atn;
    } 
    void ThreadMain()
    {
        while(all nodes you need to add)
        {
            TreeNode node = new TreeNode("text");

            // This will post a call the delegate on the main thread,
            // and not block until it returns. The second parameter is an
            // array that will be passed as the arguments for the delegate.
            ctl.BeginInvoke(atn, new object[] { node });
        }
    }
}</code>