添加一个节点和4个子节点
treeGXHelp.Nodes[].Text = textBoxDropDownHelp.Text + "的主题";

            treeGXHelp.Nodes[].Nodes[].Text = textBoxDropDownHelp.Text + "的检索内容";

            treeGXHelp.Nodes[].Nodes[].Text = textBoxDropDownHelp.Text + "的注意事项";

            treeGXHelp.Nodes[].Nodes[].Text = textBoxDropDownHelp.Text + "的视频";

            treeGXHelp.Nodes[].Nodes[].Text = textBoxDropDownHelp.Text + "的经验教训";