tikz tree fork down edge labels

Question

\documentclass{article} 
\usepackage{tikz}
\usetikzlibrary{trees}

\begin{document}

\begin{tikzpicture}[level distance=1.5cm,
level 1/.style={sibling distance=3.5cm},
level 2/.style={sibling distance=1cm},
edge from parent fork down]
\tikzstyle{every node}=[circle,draw]

\node (Root) [red] {3}
    child {
    node {1}
    child { node {4} edge from parent node[above,draw=none] {help!} }
    child { node {1} }
    child { node {3} }
}
child {
    node {2}
    child { node {3} }
    child { node {2} }
    child { node {5} }
};

\end{tikzpicture}
\end{document}

yields

but I'd like to add textual labels the positions marked with the red and blue text below.

This post somewhat addresses the red issue but not the blue issue.

Getting the (horizontally running) text along that first, short line before it splits is what is giving me the most trouble.

It seems that first stem needs to be taller to allow room for a label there, especially when the right branch will have its own label.

Answer 1

Does this illustration help to understand the relation between path operators (like -- and -|) and the pos key?

For the last example, your will need my paths.ortho library which has been developed for this reason (amongst others).

Code

\documentclass[tikz]{standalone}
\usetikzlibrary{trees}
\tikzset{level distance=1.5cm,
         level 1/.style={sibling distance=3.5cm},
         level 2/.style={sibling distance=1cm}}
\makeatletter
\def\tikz@ege@from@parent@macro@node#1#2{%
  \pgfextra{\def\tikz@@tonodes{#2}}
  [style=edge from parent, #1, /utils/exec=\tikz@node@is@a@labeltrue]
  \tikz@edge@to@parent@path}
\tikzset{
  edge from parent fork down*/.style={
    edge from parent macro=\tikz@ege@from@parent@macro@node,
    edge from parent path={(\tikzparentnode\tikzparentanchor) |-
    ([shift=(down:.5\tikzleveldistance)]
      \tikzparentnode\tikzparentanchor-|\tikzchildnode\tikzchildanchor)
      \tikz@@tonodes -- (\tikzchildnode\tikzchildanchor)}}}
\makeatother
\usetikzlibrary{paths.ortho}
\tikzset{
  edge from parent fork down ortho/.style={
    edge from parent path={{[hvvh/distance=.5\tikzleveldistance, hvvh/from center]
      (\tikzparentnode\tikzparentanchor) |-| (\tikzchildnode\tikzchildanchor)}}}}
\newcommand*\myTree[1]{%
\tikz[#1]\path [every child node/.append style={draw, circle}]
  node[every child node] (Root) [red] {3}
    child { node {1} 
      child { node {4} } child { node {1} } child { node {3} }
      edge from parent[font=\tiny] node[at start] {0} node [pos=.125] {.125}
        node[near start] {.25} node[midway] {.5} node[near end] {.75}
        node [pos=.875] {.875} node[at end] {1}}
    child { node {2}
      child { node {3} } child { node {2} } child { node {5} }
      edge from parent[font=\tiny] node[at start] {0} node [pos=.125] {.125}
        node[near start] {.25} node[midway] {.5} node[near end] {.75}
        node [pos=.875] {.875} node[at end] {1}};}
\begin{document}
\myTree{edge from parent fork down}
\myTree{edge from parent fork down*}
\myTree{edge from parent fork down ortho}
\end{document}

Output

Answer 2

Here is another approach where a internal label (A) is assigned to the ROOT which is the origin and then use shift={(x,y)} to add labels. Here the first level distance is increased a little bit to allow room for blue label. The last 3 lines tells how to add labels,

Code:

\documentclass{article} 
\usepackage[papersize={10cm,8cm}]{geometry}
\usepackage{tikz}
\usetikzlibrary{trees}

\begin{document}

\begin{tikzpicture}[level distance=2cm,
level 1/.style={sibling distance=3.5cm},
level 2/.style={sibling distance=1cm,level distance=1.5cm},
edge from parent fork down]
\tikzstyle{every node}=[circle,draw]

\node (Root) [red]  (A) {3}
    child {
    node {1}
    child { node {4} edge from parent node[above,draw=none] {help!} }
    child { node{1} }
    child { node {3} }
}
child {
    node {2}
    child { node {3} }
    child { node{2} }
    child { node {5} }
};
\node [draw=none,blue,shift={(2.1cm,-0.5cm)}] (A) {Horizontal label here};
\node [draw=none,red, shift={(-1cm,-0.8cm)}] (A) {here A};
\node [draw=none,red, shift={( 1cm,-0.8cm)}] (A) {here B};
\end{tikzpicture}
\end{document}