% -*- mode: latex -*-
\begin{tikzpicture}
  \newcommand{\databox}[1]{\parbox{2.5em}{\centering data #1}}
  \newcommand{\withbox}[1]{\parbox{3em}{\centering model #1}}

  \node (root) {root}[
  level 1/.style={sibling distance=7em},
  level 2/.style={sibling distance=3.5em},
  level distance=3em,
  ]
  child {
    node (data1) {\databox{x = 1}}
    child {node (t2mb1) {test A}
      child {node (t2mb1a) {\withbox{\modelname{X}}}}
      child {node (t2mb1b) {\withbox{\modelname{Y}}}}
    }
    child {node (t1mb1) {test B}}
  }
  child  {
    node (data2) {\databox{x = 2}}
    child {node (t2mb2) {test A}
      child {node (t2mb2a) {\withbox{\modelname{X}}}}
      child {node (t2mb2b) {\withbox{\modelname{Y}}}}
    }
    child {node (t1mb2) {test B}}
  };
\end{tikzpicture}