\documentclass[border=10pt,multi,tikz]{standalone}
\usepackage[linguistics]{forest}
\forestset{pad/.style={minimum width=5em}}
\begin{document}
\begin{forest}
nice empty nodes
[S
[{every linguist}
]
[
[1, pad
]
[S
[ John
]
[
[T, pad
]
[VP
[V\\introduced
]
[DP\\$t_{1}$, calign with current
]
[PP\\{to Mary}
]
]
]
]
]