{
            TreeNode parent = treeView1.SelectedNode.Parent;
            TreeNode selected_node = treeView1.SelectedNode;
            TreeNode prev_node = selected_node.PrevNode;
            if (prev_node != null)
            {
                selected_node.Remove();
                parent.Nodes.Insert(prev_node.Index, selected_node);    
                treeView1.SelectedNode = selected_node;
            }
}

public class TreeViewSort
    {
        TreeView _treeView;
        ArrayList _nodes;
        CompareNodes _proc;

        public delegate int CompareNodes(TreeNode node1, TreeNode node2);

        public TreeViewSort(TreeView treeView, CompareNodes proc)
        {
            _treeView = treeView;
            _proc = proc;
        }

        public void SortChildren(TreeNode parentNode)
        {
            _nodes = new ArrayList();
            int index = 0;
            foreach (TreeNode childNode in parentNode.Nodes)
            {
                _nodes.Add(childNode);

                TVITEM item = new TVITEM();
                item.mask = TVIF_PARAM;
                item.hItem = childNode.Handle;
                item.lParam = index++;
                item.cChildren = 0;
                item.cchTextMax = 0;
                item.iImage = item.iSelectedImage = 0;
                item.state = item.stateMask = 0;
                item.pszText = IntPtr.Zero;

                IntPtr ptrTVITEM = Marshal.AllocHGlobal(Marshal.SizeOf(item));
                Marshal.StructureToPtr(item, ptrTVITEM, false);

                SendMessage(_treeView.Handle, TVM_SETITEM, 0, ptrTVITEM);

                Marshal.FreeHGlobal(ptrTVITEM);
            }

            GCHandle handleThis = GCHandle.Alloc(this);

            TVSORTCB sort = new TVSORTCB();
            sort.hParent = parentNode.Handle;
            sort.lpfnCompare = new CompareNodesImplDelegate(CompareNodesImpl);
            sort.lParam = (IntPtr)handleThis;

            IntPtr ptrTVSORTCB = Marshal.AllocHGlobal(Marshal.SizeOf(sort));
            Marshal.StructureToPtr(sort, ptrTVSORTCB, false);

            SendMessage(_treeView.Handle, TVM_SORTCHILDRENCB, 0, ptrTVSORTCB);

            handleThis.Free();
            Marshal.FreeHGlobal(ptrTVSORTCB);
        }

        const int TV_FIRST = 0x1100;
        const int TVM_SORTCHILDRENCB = TV_FIRST + 21;
        const int TVM_SETITEM = 4415;
        const int TVIF_PARAM = 0x0004;

        [StructLayout(LayoutKind.Sequential)]
        struct TVSORTCB
        {
            public IntPtr hParent;
            public CompareNodesImplDelegate lpfnCompare;
            public IntPtr lParam;
        }

        [DllImportAttribute("user32.dll", CharSet=CharSet.Auto)]
        static extern IntPtr SendMessage(IntPtr hWnd, int msg, int wParam, IntPtr lParam);

        [StructLayout(LayoutKind.Sequential)]
        struct TVITEM
        {
            public uint   mask;
            public IntPtr hItem;
            public uint   state;
            public uint   stateMask;
            public IntPtr pszText;
            public int    cchTextMax;
            public int    iImage;
            public int    iSelectedImage;
            public int    cChildren;
            public int      lParam;
        }

        delegate int CompareNodesImplDelegate(
            int lParam1, int lParam2, IntPtr lParamSort);

        static int CompareNodesImpl(int lParam1, int lParam2, IntPtr lParamSort)
        {
            TreeViewSort host = (TreeViewSort)((GCHandle)lParamSort).Target;
            //Some bug. Проявляется иногда при удалении единственного контрола
            if (lParam1 >= host._nodes.Count)
                return 1;    //Move lParam1 to the end
            if (lParam2 >= host._nodes.Count)
                return -1;    //Move lParam2 to the end
            return host._proc((TreeNode)host._nodes[lParam1], (TreeNode)host._nodes[lParam2]);
        }
    }