System.Windows.Forms.TreeView.ExpandAll C# (CSharp) Method

        public void ExpandAll()
        {
            for (int i = 0; i < Nodes.Count; i++)
                Nodes[i].ExpandAllInternal();
            Refresh();
        }
        public TreeNode Find(Predicate<TreeNode> match)

 private void fillTreeTeachers()
 {
     _treeView1.BeginUpdate();
     foreach (Teacher teacher in AppForm.CURR_OCTT_DOC.TeachersRootNode.Nodes)
     {
         TreeNode tn = new TreeNode(teacher.getTreeText());
         tn.Tag = teacher;
         _treeView1.Nodes.Add(tn);
     }
     _treeView1.ExpandAll();
     _treeView1.EndUpdate();
     this.Refresh();
 }