Tikz: drawing a taxonomy/classification figure - latex

Question

I'm using TikZ for the first time and I don't know how to draw this taxonomy figure.
I only managed to draw 2 columns, with the following code:
\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{shapes,snakes,positioning,shapes.misc}
\begin{document}
\begin{tikzpicture}
\node at (-3,1) [rectangle, aspect=0.5, draw=black!60,fill=black!20, inner sep=3pt, text width=2cm,,align=center](a){text text text};
\node at (-9,-1) [rectangle,draw](b1){text2};
\node at (-8.7,-2) [rectangle,draw](b2){text3};
\node at (-8.7,-3) [rectangle,draw](b3){text4};
\node at (-8.7,-4) [rectangle,draw](b4){text5};
\node at (-8.7,-5) [rectangle,draw](b5){text6};
\draw[->,thick] (a)--(0,0)--(-9,0);
\draw[->,thick] (-9,0)--(b1);
\draw[->,thick] ([xshift=0cm,yshift=0cm]b1.210)|-([]b2.west);
\draw[->,thick] ([xshift=0cm,yshift=0cm]b1.210)|-([]b3.west);
\draw[->,thick] ([xshift=0cm,yshift=0cm]b1.210)|-([]b3.west);
\draw[->,thick] ([xshift=0cm,yshift=0cm]b1.210)|-([]b4.west);
\draw[->,thick] ([xshift=0cm,yshift=0cm]b1.210)|-([]b5.west);
%%%%%%%%%%%%%%%%%%%%%%%
\node at (5,-1) [rectangle,draw](c1){text2};
\node at (4.7,-2) [rectangle,draw](c2){text3};
\node at (4.7,-3) [rectangle,draw](c3){text4};
\draw[->,thick] (a)--(0,0)--(5,0);
\draw[->,thick] (5,0)--(c1);
\draw[->,thick] ([xshift=0cm,yshift=0cm]c1.330)|-([]c2.east);
\draw[->,thick] ([xshift=0cm,yshift=0cm]c1.330)|-([]c3.east);
\end{tikzpicture}
\end{document}

Answer 1

You can use the forest package instead of trying to draw it manually with tikz. Then, it's easier to change the actual content (node, number of columns, etc.):
\documentclass[tikz,border=10pt]{standalone}
\usetikzlibrary{arrows.meta}
\usepackage{forest}
\begin{document}
\begin{forest}
for tree={
line width=0.5pt,
draw=black,
fit=rectangle,
edge={color=black,>={Triangle[]}, ->},
if level=0{%
l sep+=1cm,
for descendants={%
calign=first,
},
align=center,
parent anchor=south,
}{%
if level=1{%
parent anchor=south west,
child anchor=north,
tier=three ways,
align=center,
for descendants={%
child anchor=west,
parent anchor=west,
align=left,
anchor=west,
xshift=-20pt,
edge path={
\noexpand\path[\forestoption{edge}]
(!to tier=three ways.parent anchor) |-
(.child anchor)\forestoption{edge label};
},
},
}{}%
},
}
[Drawing Diagrams
[Operational
[Offloading\\method
[Cost\\benefit\\analysis
[Mobility\\management
[Connection\\protocol]
]
]
]
]
[End user
[Incentives
[Presentation\\and usability]
]
]
[Service level
[Performance
[Cloud APIs]
]
]
]
\end{forest}
\end{document}