TreeForm without overlap - graph

Question

I sometimes run into the problem of labels in TreeForm being unreadable because of overlap. An example is below, can anyone see a way to get rid of overlap?
{{4, 5, 6}, {{{2, 4, 5, 6}, {{{1, 2, 4}, {}}, {{2, 3, 6}, {}}}}, {{4,
5, 6, 8}, {{{4, 7, 8}, {}}, {{6, 8, 9}, {}}}}}} // TreeForm
(source: yaroslavvb.com)
Belisarius' solution helps with overlap, but loses Tooltips, ie compare with
TreeForm[Hold[
GraphPlotHighlight[edges : {((_ -> _) | {_ -> _, _}) ...},
hl : {___} : {}, opts : OptionsPattern[]] :=
Module[{verts, coords, g, sub}, 5]]]
(source: yaroslavvb.com)
Answer update 11/12
I ended up using code below (belisarius' code with a minor fix)
myTreeForm[exp_] :=
Module[{tooltipText, i},
tooltipText =
Cases[Cases[MakeBoxes[TreeForm#exp, StandardForm],
TooltipBox[x__] -> x, 7, Heads -> True],
TagBox[x__, y__] -> DisplayForm[First#{x}], Heads -> True];
i = 0;
TreeForm[exp,
VertexRenderingFunction -> ({Tooltip[
Inset[Rasterize[Text[" " <> ToString##2 <> " "],
Background -> LightBlue], #1], tooltipText[[i++]]]} &)]];

Answer 1

I did this before, but never generalized the result.
rectOffset = {.25,.1};
fontSize = 10
TreeForm[list,
VertexRenderingFunction -> ({White, EdgeForm[Black],
Rectangle[#1 - rectOffset, #1 + rectOffset], Black,
Text[ Style[#2, fontSize], #1]} &)]
Edit With Tooltips
Using a "different approach"
Code is dirty, sorry no time to clean it up right now
rectOffset = {.33, .1};
fontSize = 9;
p = Cases[
Cases[MakeBoxes[TreeForm#list, StandardForm], TooltipBox[x__] -> x,
7, Heads -> True], TagBox[x__, y__] -> DisplayForm[First#{x}],
Heads -> True];
i = 0;
TreeForm[list,
VertexRenderingFunction -> ({White, EdgeForm[Black],
Rectangle[#1 - rectOffset, #1 + rectOffset], Black,
Tooltip[Text[Style[#2, fontSize], #1], p[[i++]]]} &)]
Output
Edit 2
I think this version is better:
Clear["Global`*"];
list = Hold[
GraphPlotHighlight[edges : {((_ -> _) | {_ -> _, _}) ...},
hl : {___} : {}, opts : OptionsPattern[]] :=
Module[{verts, coords, g, sub}, 5]];
myTreeForm[exp_] :=
Module[{ps, tooltipText, i},
ps[text_] := Rasterize[Text[Style[text]], "RasterSize"];
tooltipText =
Cases[Cases[MakeBoxes[TreeForm#list, StandardForm],
TooltipBox[x__] -> x, 7, Heads -> True],
TagBox[x__, y__] -> DisplayForm[First#{x}], Heads -> True];
i = 0;
TreeForm[list,
EdgeRenderingFunction -> ({Red, Line[#1]} &),
VertexRenderingFunction -> ({White, EdgeForm[Black], {}, Black,
Tooltip[
Inset[Rasterize[Text[" " <> ToString##2 <> " "],
Background -> LightBlue], #1], tooltipText[[i++]]]} &)]
];
list // myTreeForm
Output:
Edit 4 ... and last one
Cleaned up code, remove spurious functions and variables that were there just to complicate things:
myTreeForm[list_] := Module[{tooltipText, i},
tooltipText =
Cases[Cases[MakeBoxes[TreeForm#list, StandardForm],
TooltipBox[x__] -> x, 7, Heads -> True],
TagBox[x__, y__] -> DisplayForm[First#{x}], Heads -> True];
i = 0;
TreeForm[list,
VertexRenderingFunction ->
({Tooltip[Inset[Rasterize[Text[" " <> ToString##2 <> " "],
Background -> LightBlue], #1], tooltipText[[i++]]]} &)
]
];
HTH!

Answer 2

It looks as if the option VertexCoordinateRules may be your best hope.