\documentclass[class=minimal,border=0pt]{standalone}

\usepackage{tikz}
\usepackage{fontspec}

\setmainfont[
  Scale=0.90,
  BoldFeatures={Scale=1.0}
]{Open Sans}

\begin{document}

\begin{tikzpicture}[
    every node/.style={circle, fill=black, minimum size=3mm},
    start/.style={draw=black, very thick, fill=none, minimum size=6mm, node font=\bfseries},
    end/.style={draw=black, double, very thick, fill=none, minimum size=7mm, node font=\bfseries}
]
  \node [start] (S) at  (0,-2)     {?};

  \node [draw]  (a) at  (0,-1)     {}  edge    [dashed]    (S);
  \node [draw]  (b) at  (0,-0)     {}  edge    [-]         (a);
  \node [draw]  (c) at  (1,-1)     {}  edge    [-]         (a);
  \node [draw]  (d) at  (2,0)      {}  edge    [-]         (b)
                                       edge    [-]         (c);

  \node [draw]  (e) at  (0,-3)     {}  edge    [dashed]    (S);
  \node [draw]  (f) at  (0,-5.5)   {}  edge    [-]         (e);
  \node [draw]  (g) at  (4.5,-5.5) {}  edge    [-]         (f);
  \node [draw]  (h) at  (4.5,-2)   {}  edge    [-]         (g);
  \node [draw]  (i) at  (4.5,-1)   {}  edge    [-]         (h);

  \node [draw]  (j) at  (1,-3)     {}  edge    [dashed]    (S)
                                       edge    [-]         (e);
  \node [draw]  (k) at  (1,-5)     {}  edge    [-]         (j);
  \node [draw]  (l) at  (2,-4)     {}  edge    [-]         (k);
  \node [draw]  (m) at  (3,-5)     {}  edge    [-]         (k);
  \node [draw]  (n) at  (3,-4)     {}  edge    [-]         (l)
                                       edge    [-]         (m);
  \node [draw]  (o) at  (3,-3)     {}  edge    [-]         (n);
  \node [draw]  (p) at  (4,-3)     {}  edge    [-]         (n);
  \node [draw]  (q) at  (3,-2)     {}  edge    [-]         (o)
                                       edge    [-]         (p);
  \node [draw]  (v) at  (4,-5)     {}  edge    [-]         (p);
  \node [draw]  (r) at  (1,-2)     {}  edge    [-]         (e)
                                       edge    [-]         (n);
  \node [draw]  (t) at  (2,-1)     {}  edge    [-]         (r);
  \node [draw]  (u) at  (2,-2)     {}  edge    [-]         (t)
                                       edge    [-]         (q);
  
  \node [end]   (end) at (3,-1)    {}  edge    [-]         (d)
                                       edge    [-]         (i)
                                       edge    [-]         (q);
  \node [draw]  (w) at  (4,0)      {}  edge    [-]         (end);
\end{tikzpicture}

\end{document}