% Horizontal tree: level distance must exceed ~half parent + half child width or nodes overlap (resizebox does not fix that).
\begin{tikzpicture}[
  grow=right,
  level distance=30mm,
  sibling distance=23mm,
  decision/.style={
    rectangle,
    draw,
    rounded corners=1.5pt,
    align=center,
    inner sep=1.2pt,
    minimum width=14mm,
    minimum height=4.8mm,
    font=\scriptsize,
  },
  leaf/.style={
    rectangle,
    draw,
    align=center,
    inner sep=1.2pt,
    text width=19mm,
    minimum height=4mm,
    font=\scriptsize,
  },
  edge from parent/.style={draw, -{Latex[length=1.2mm]}},
]
\node[decision] {Participant}
  child {
    node[decision] {Platform: Hotel}
      child {node[leaf] {Task sampled\\from hotel pool}}
  }
  child {
    node[decision] {Platform: Airline}
      child {node[leaf] {Task sampled\\from airline pool}}
  };
\end{tikzpicture}
