dia2.tex

    \begin{tikzpicture}[-latex,
every node/.style = {shape=rectangle, line width=1pt, color=black,
  draw, align=center, text width=2.5em, minimum height=1.5em,
  blur shadow={shadow blur extra rounding, shadow xshift=2pt, shadow yshift=-2pt},
  fill=boxbg},
witness/.style = {
  postaction = { pattern=north west lines }, pattern color=boxredish
},
note/.style = {
  fill=none, color=white, text width=20em, blur shadow={shadow opacity=0}, text=black
},
  edge from parent/.style = {line width=1pt, draw},
level 1/.style={sibling distance=7.5em},
level 2/.style={sibling distance=4em},
level 3/.style={sibling distance=3.5em},
level distance=2.75em
]
\node (root) [fill=boxredish] {$a$}
  child { node [witness] {${w^x_t}_1$}
    child { node {} }
    child { node {} }
  }
  child { node {}
    child { node [fill=boxlime] {$x$} }
    child { node [witness] {${w^x_t}_0$} }
  };

\node [above of=root, yshift=-1em, draw, note] {{\footnotesize accumulator value}};

\end{tikzpicture}