I'm translating a manual of syntax and they have some examples of non-valid structures. The first one I was able to reproduce, but not the second.
This is what I'm trying to reproduce:
My current code is the following:
\documentclass{article}
\usepackage{tikz-qtree}
\begin{document}
\begin{figure}[h]
\centering
\textbf{a}) \begin{tikzpicture}[level distance=30pt,sibling distance=5mm]
\tikzset{every tree node/.style={align=center,anchor=base}}
\tikzset{level 1+/.style={level distance=2\baselineskip}}
\tikzset{frontier/.style={distance from root=6\baselineskip}}
\Tree [.a [.b ] [.c ] ]
\begin{scope}[grow'=up,yshift=-1.7cm]
\Tree [.d [.b ] [.c ] ]
\end{scope}
\end{tikzpicture}\qquad
\textbf{b}) \begin{tikzpicture}[level distance=30pt,sibling distance=5mm]
\Tree ??????????????????
\end{figure}
\end{document}