public static class BTreePrinter
{
    class NodeInfo
    {
        public BNode Node;
        public string Text;
        public int StartPos;
        public int Size { get { return Text.Length; } }
        public int EndPos { get { return StartPos + Size; } set { StartPos = value - Size; } }
        public NodeInfo Parent, Left, Right;
    }

    public static void Print(this BNode root, int topMargin = 2, int leftMargin = 2)
    {
        if (root == null) return;
        int rootTop = Console.CursorTop + topMargin;
        var last = new List<NodeInfo>();
        var next = root;
        for (int level = 0; next != null; level++)
        {
            var item = new NodeInfo { Node = next, Text = next.item.ToString(" 0 ") };
            if (level < last.Count)
            {
                item.StartPos = last[level].EndPos + 1;
                last[level] = item;
            }
            else
            {
                item.StartPos = leftMargin;
                last.Add(item);
            }
            if (level > 0)
            {
                item.Parent = last[level - 1];
                if (next == item.Parent.Node.left)
                {
                    item.Parent.Left = item;
                    item.EndPos = Math.Max(item.EndPos, item.Parent.StartPos);
                }
                else
                {
                    item.Parent.Right = item;
                    item.StartPos = Math.Max(item.StartPos, item.Parent.EndPos);
                }
            }
            next = next.left ?? next.right;
            for (; next == null; item = item.Parent)
            {
                Print(item, rootTop + 2 * level);
                if (--level < 0) break;
                if (item == item.Parent.Left)
                {
                    item.Parent.StartPos = item.EndPos;
                    next = item.Parent.Node.right;
                }
                else
                {
                    if (item.Parent.Left == null)
                        item.Parent.EndPos = item.StartPos;
                    else
                        item.Parent.StartPos += (item.StartPos - item.Parent.EndPos) / 2;
                }
            }
        }
        Console.SetCursorPosition(0, rootTop + 2 * last.Count - 1);
    }

    private static void Print(NodeInfo item, int top)
    {
        SwapColors();
        Print(item.Text, top, item.StartPos);
        SwapColors();
        if (item.Left != null)
            PrintLink(top + 1, "┌", "┘", item.Left.StartPos + item.Left.Size / 2, item.StartPos);
        if (item.Right != null)
            PrintLink(top + 1, "└", "┐", item.EndPos - 1, item.Right.StartPos + item.Right.Size / 2);
    }

    private static void PrintLink(int top, string start, string end, int startPos, int endPos)
    {
        Print(start, top, startPos);
        Print("─", top, startPos + 1, endPos);
        Print(end, top, endPos);
    }

    private static void Print(string s, int top, int left, int right = -1)
    {
        Console.SetCursorPosition(left, top);
        if (right < 0) right = left + s.Length;
        while (Console.CursorLeft < right) Console.Write(s);
    }

    private static void SwapColors()
    {
        var color = Console.ForegroundColor;
        Console.ForegroundColor = Console.BackgroundColor;
        Console.BackgroundColor = color;
    }
}