tik.tex

\documentclass{standalone}
\usepackage{tikz}
\begin{document}
   \begin{tikzpicture}
      [sibling distance=30em,level distance=6em,
      every node/.style={shape=rectangle,draw,align=center}]
\node[font = {\huge\bfseries},red]{1,2,3 electron system}
   child{node[font = {\Large\bfseries},black]{Exact Approach}
      child{node[font = {\Large\bfseries},black]{compute many body WF and density}
        child{node[font = {\Large\bfseries},black]{exact observable }}}}
   child{node[font = {\Large\bfseries},blue]{Approximate approaches }
      child{node[font = {\Large\bfseries},blue]{approximate the WF and density}
        child{node[font = {\Large\bfseries},blue]{approximate observable}}}};
   \end{tikzpicture}
\end{document}