Produce nice TIKZ picture (Tree)

Question

so far i have the following code which gives me a ugly TIKZ picture (twe level tree). Is there a comfortable way to get a nice spacing for second level nodes? Thank you very much in advance!

\documentclass[a4paper,12pt,titlepage]{scrreprt}
 % \documentclass[a4paper,11pt, twoside]{scrartcl}

\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage[english, ngerman]{babel}
\usepackage{graphicx}
% \usepackage[pdftex]{graphicx}
% \usepackage{epstopdf}
\usepackage{latexsym}
\usepackage{amsmath,amssymb, amsthm}
\usepackage{tikz}
\usetikzlibrary{external}
%\tikzexternalize % activate!
\usepackage{lscape}
\usepackage{fullpage}
\usetikzlibrary{positioning,shadows,arrows,trees,shapes,fit}

\begin{document}
\pagestyle{empty}
\begin{landscape}
\begin{figure}[h]
\begin{center}
\begin{tikzpicture}
[level distance=2.5cm,
level 1/.style={sibling distance=5cm},
level 2/.style={sibling distance=2cm}, auto,transform shape ]
\tikzstyle{every node}=[rectangle,draw]
\node(Root) {Gesamtdaten}
    child { node (Root-0){$RR=0$} }
    child {
        node (Root-1){$RR\neq 0$}
        child { node(Root-1-1) {$0<RR\leq 0.25$} }
        child { node (Root-1-2){$0.25<RR\leq 0.65$} }
        child { node (Root-1-3){$0.65 < RR \leq 1$} }
        child { node(Root-1-4) {$1 < RR \leq 1.2$} }
        child { node (Root-1-5){$1.2 < RR \leq 1.35$} }
        child { node (Root-1-6){$1.35 < RR \leq 1.5$} }
        child { node (Root-1-7){$1.5 < RR \leq 1.7$} }
        child { node (Root-1-8){$1.7 < RR \leq 1.95$} }
        child { node (Root-1-9){$1.95 < RR \leq 2.4$} }
        child { node (Root-1-10){$2.4 < RR \leq 3$} }
        }
;
\begin{scope}[every node/.style={right}]
 \path (Root-0    -| Root-1)  ++(2cm,0) node[color=red] {SVM 1};
 \path (Root-1-1  -| Root-1-10) ++(2cm,0) node [color=red] {SVM 2};
 \end{scope}
\end{tikzpicture}

\end{center}
\end{figure}
\end{landscape}

\end{document}

Answer 1

This is a variation on smoneck's answer which implements the east-growing tree in forest.

I begin by demonstrating forest's ability to space the children automatically even without additional hints.

Initial conversion

forest uses the bracket syntax which simplifies the definition of the tree somewhat:

\documentclass[tikz,12pt]{standalone}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage[english, ngerman]{babel}
\usepackage{forest}
\usetikzlibrary{positioning}

\begin{document}
  \begin{forest}
    for tree={
      draw,
    }
    [Gesamtdaten, name=Root
      [{$RR=0$}, name=Root-0
      ]
      [{$RR\neq 0$}, name=Root-1
        [{$0<RR\leq 0.25$}, name=Root-1-1
        ]
        [{$0.25<RR\leq 0.65$}, name=Root-1-2
        ]
        [{$0.65 < RR \leq 1$}, name=Root-1-3
        ]
        [{$1 < RR \leq 1.2$}, name=Root-1-4
        ]
        [{$1.2 < RR \leq 1.35$}, name=Root-1-5
        ]
        [{$1.35 < RR \leq 1.5$}, name=Root-1-6
        ]
        [{$1.5 < RR \leq 1.7$}, name=Root-1-7
        ]
        [{$1.7 < RR \leq 1.95$}, name=Root-1-8
        ]
        [{$1.95 < RR \leq 2.4$}, name=Root-1-9
        ]
        [{$2.4 < RR \leq 3$}, name=Root-1-10
        ]
      ]
    ]
    \begin{scope}[every node/.style={right}]
      \path (Root-0    -| Root-1)  ++(2cm,0) node[color=red] {SVM 1};
      \path (Root-1-1  -| Root-1-10) ++(2cm,0) node [color=red] {SVM 2};
    \end{scope}
  \end{forest}

\end{document}

This spaces the nodes but unfortunately does not guarantee that the connecting lines will not cross nodes, especially when the nodes' borders are drawn.

Tweaking the appearance

We add to l to increase the distance between levels, thicken the lines drawn throughout, and use -| type line construction to draw the connecting lines.

\documentclass[tikz,12pt]{standalone}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage[english, ngerman]{babel}
\usepackage{forest}
\usetikzlibrary{positioning}

\begin{document}
  \begin{forest}
    for tree={
      draw,
      thick,
      l sep=40pt,
      edge path={
        \noexpand\path[thick, -, \forestoption{edge}]
          (!u.parent anchor) -- +(0,-25pt) -|
          (.child anchor)\forestoption{edge label};
      },
    }
    [Gesamtdaten, name=Root
      [{$RR=0$}, name=Root-0
      ]
      [{$RR\neq 0$}, name=Root-1
        [{$0<RR\leq 0.25$}, name=Root-1-1
        ]
        [{$0.25<RR\leq 0.65$}, name=Root-1-2
        ]
        [{$0.65 < RR \leq 1$}, name=Root-1-3
        ]
        [{$1 < RR \leq 1.2$}, name=Root-1-4
        ]
        [{$1.2 < RR \leq 1.35$}, name=Root-1-5
        ]
        [{$1.35 < RR \leq 1.5$}, name=Root-1-6
        ]
        [{$1.5 < RR \leq 1.7$}, name=Root-1-7
        ]
        [{$1.7 < RR \leq 1.95$}, name=Root-1-8
        ]
        [{$1.95 < RR \leq 2.4$}, name=Root-1-9
        ]
        [{$2.4 < RR \leq 3$}, name=Root-1-10
        ]
      ]
    ]
    \begin{scope}[every node/.style={right}]
      \path (Root-0    -| Root-1)  ++(2cm,0) node[color=red] {SVM 1};
      \path (Root-1-1  -| Root-1-10) ++(2cm,0) node [color=red] {SVM 2};
    \end{scope}
  \end{forest}

\end{document}

Not only is this much too large for landscape A4, it also looks a bit squashed given the length of the final line compared with the height of the tree. So it seems worth seeing what the growth direction suggested by smoneck might do for us.

The final tree

\documentclass[tikz,12pt]{standalone}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage[english, ngerman]{babel}
\usepackage{forest}
\usetikzlibrary{positioning}

\begin{document}
  \begin{forest}
    for tree={
      draw,
      thick,
      l sep=40pt,
      edge path={
        \noexpand\path[thick, -, \forestoption{edge}]
          (!u.parent anchor) -- +(20pt,0) |-
          (.child anchor)\forestoption{edge label};
      },
      grow'=east,
      child anchor=west,
      parent anchor=east,
      anchor=west,
    }
    [Gesamtdaten, name=Root
      [{$RR=0$}, name=Root-0
      ]
      [{$RR\neq 0$}, name=Root-1
        [{$0<RR\leq 0.25$}, name=Root-1-1
        ]
        [{$0.25<RR\leq 0.65$}, name=Root-1-2
        ]
        [{$0.65 < RR \leq 1$}, name=Root-1-3
        ]
        [{$1 < RR \leq 1.2$}, name=Root-1-4
        ]
        [{$1.2 < RR \leq 1.35$}, name=Root-1-5
        ]
        [{$1.35 < RR \leq 1.5$}, name=Root-1-6
        ]
        [{$1.5 < RR \leq 1.7$}, name=Root-1-7
        ]
        [{$1.7 < RR \leq 1.95$}, name=Root-1-8
        ]
        [{$1.95 < RR \leq 2.4$}, name=Root-1-9
        ]
        [{$2.4 < RR \leq 3$}, name=Root-1-10
        ]
      ]
    ]
    \begin{scope}[every node/.style={red}]
      \node [above=5pt of Root-0] {SVM 1};
      \node [above=5pt of Root-1-1] {SVM 2};
    \end{scope}
  \end{forest}

\end{document}

The result is 107x97mm which will easily fit A4.

Answer 2

What about putting it sideways? I basically added the grow and edge from parent path options and adjusted the distances. You could also play with the font and/or scale.

You just need to adjust the scope-section.

\begin{tikzpicture}
    [grow=right, scale=1.,font=\normalsize,
    edge from parent path={(\tikzparentnode.east) |- (\tikzchildnode.west)},
    level distance=3.5cm,
    level 1/.style={sibling distance=6cm},
    level 2/.style={sibling distance=1.2cm, level distance=3.5cm},
    auto,transform shape]
\tikzstyle{every node}=[rectangle,draw]
\node(Root) {Gesamtdaten}
child { node (Root-0){$RR=0$} }
child {
node (Root-1){$RR\neq 0$}
child { node(Root-1-1) {$0<RR\leq 0.25$} }
child { node (Root-1-2){$0.25<RR\leq 0.65$} }
child { node (Root-1-3){$0.65 < RR \leq 1$} }
child { node(Root-1-4) {$1 < RR \leq 1.2$} }
child { node (Root-1-5){$1.2 < RR \leq 1.35$} }
child { node (Root-1-6){$1.35 < RR \leq 1.5$} }
child { node (Root-1-7){$1.5 < RR \leq 1.7$} }
child { node (Root-1-8){$1.7 < RR \leq 1.95$} }
child { node (Root-1-9){$1.95 < RR \leq 2.4$} }
child { node (Root-1-10){$2.4 < RR \leq 3$} }
};
%\begin{scope}[every node/.style={right}]
%\path (Root-0-| Root-1)++(2cm,0) node[color=red] {SVM 1};
%\path (Root-1-1-| Root-1-10) ++(2cm,0) node [color=red] {SVM 2};
%\end{scope}
\end{tikzpicture}