[Tex/LaTex] Prevent tikz tree nodes from overlapping

tikz-nodetikz-pgftikz-trees

I'm drawing tree structures of sentences with tikz, where nodes contain words, which may be longer sometimes. If that occurs, they are likely to overlap with neighbouring nodes. How can I tell tikz to keep a minimum spacing between neighbouring nodes? My MWE:

\documentclass{standalone}

\usepackage{tikz}
\tikzset{
  treenode/.style = {align=center, inner sep=3pt, text centered,
    font=\sffamily},
  arn_n/.style = {treenode, rectangle, text width=3em},
  arn_x/.style = {treenode},
  gray-arrow/.style = {draw=gray}
}
\usetikzlibrary{arrows}

\begin{document}
\begin{tikzpicture}[->,>=stealth',level/.style={sibling distance = 10cm/#1,
  level distance = 1cm}] 
\node [arn_n]{NP}
child { node [arn_n] {N'}
    child { node [arn_n] {N'}
        child { node [arn_n] {aa}
            child { node [arn_x] {der}
            }
        }
        child { node [arn_n] {N'}
            child { node [arn_n] {AP}
                child { node [arn_x] {geduldigsten}
                }
            }
            child { node [arn_n] {N'}
                child { node [arn_n] {N}
                    child { node [arn_x] {Konservativen}
                    }
                }
            }
        }
    }
    child { node [arn_n] {N'}
        child { node [arn_n] {aa}
            child { node [arn_x] {unserer}
            }
        }
        child { node [arn_n] {N'}
            child { node [arn_n] {N}
                child { node [arn_x] {Partei}
                }
            }
        }
    }
}
;
\end{tikzpicture}
\end{document}

Rendered MWE

In this case, the nodes containing "unserer" and "N'" overlap on the fifth level. What's a smart way to prevent that?

Best Answer

forest does it for you:

\documentclass{standalone}
\usepackage{forest}
\usetikzlibrary{arrows.meta}

\begin{document}
\begin{forest}
for tree={
  treenode/.style = {align=center, inner sep=3pt, 
        text centered, font=\sffamily},
  arn_n/.style = {treenode, rectangle, text width=3em},
  arn_x/.style = {treenode},
  gray-arrow/.style = {draw=gray},
  edge=-{Stealth}}
[NP, arn_n
    [N', arn_n
        [N', arn_n
            [aa, arn_n
                [der, arn_x]]
            [N', arn_n
                [AP, arn_n
                    [geduldigsten, arn_x]]
                [N', arn_n
                    [N, arn_n
                        [Konservativen, arn_x]]]]]
        [N', arn_n
            [aa, arn_n
                [unserer, arn_x]]
            [N', arn_n
                [N, arn_n
                    [Partei, arn_x]]]]]]
\end{forest}
\end{document}

enter image description here