\documentclass[12pt]{standalone}
\usepackage[linguistics]{forest}
%\forestset{for tree={outer sep=0pt,inner sep=0pt}} % why can't I do this
\begin{document}
\begin{forest}for tree={outer sep=0pt,inner sep=0pt} % when I can do this?
[TP [DP [the man with the hat ,roof ]]
[T’
[T\\will ]
[VP [{go to the store tomorrow},roof ] ]
]
]
\end{forest}
\end{document}