I do not find anywhere how to specify vertical alignment for a forest obtained with the forest package. Here is an example of a table I'd like to have in a document:
\documentclass[a4paper]{report}
\usepackage{amsmath}
\usepackage{tikz}
\usepackage{forest}
\usepackage{booktabs}
\begin{document}
\centering
\begin{tabular}{c@{\hskip 20pt}|cc@{\hskip 20pt}cc@{\hskip 20pt}cc}
\toprule
Derivative & $\tau$ & $F(\tau)$ & $\tau$ & $F(\tau)$ & $\tau$ & $F(\tau)$\
\cmidrule{1-7}
$y'$ & \begin{forest} for tree = {circle,draw,fill,inner sep=1pt} [] \end{forest} & $f$ & & & & \
\cmidrule{1-7}
$y''$ & \begin{forest} for tree = {circle,draw,fill,grow=north,l=4pt,inner sep=1pt} [[]] \end{forest} & $f'f$ & & & & \
\cmidrule{1-7}
$y^{(3)}$ & \begin{forest} for tree = {circle,draw,fill,grow=north,l=4pt,inner sep=1pt} [[][]] \end{forest} & $f''(f,f)$ & \begin{forest} for tree = {circle,draw,fill,grow=north,l=4pt,inner sep=1pt} [[[]]] \end{forest} & $f''(f,f)$\
\cmidrule{1-7}
$y^{(4)}$ & \begin{forest} for tree = {circle,draw,fill,grow=north,l=4pt,inner sep=1pt} [[][][]] \end{forest} & $f^{(3)}(f,f,f)$ &
\begin{forest} for tree = {circle,draw,fill,grow=north,l=4pt,inner sep=1pt} [[[]][]] \end{forest} & $f''(f,f'f)$ &
\begin{forest} for tree = {circle,draw,fill,grow=north,l=4pt,inner sep=1pt} [[][[]]] \end{forest} & $f''(f'f,f)$ \[10pt]
& \begin{forest} for tree = {circle,draw,fill,grow=north,l=4pt,inner sep=1pt} [[[[]]]] \end{forest} & $f'f'f'f$ &
\begin{forest} for tree = {circle,draw,fill,grow=north,l=4pt,inner sep=1pt} [[[][]]] \end{forest} & $f'f''(f, f)$ &
\begin{forest} for tree = {circle,draw,fill,grow=north,l=4pt,inner sep=1pt} [[][[]]] \end{forest} & $f''(f'f,f)$ \
\bottomrule
\end{tabular}
\end{document}
Which results in
I would like to have, for example in the second line, that the $f'f$ is aligned with the center of its corresponding tree, and not with the root.
