\begin{tikzpicture}[
  level distance=13mm,
  every node/.style={font=\small},
  inner/.style={draw, circle, minimum size=7mm, inner sep=0pt},
  leaf/.style={draw, rectangle, minimum width=9mm, minimum height=6mm, inner sep=1pt},
  level 1/.style={sibling distance=52mm},
  level 2/.style={sibling distance=26mm},
  level 3/.style={sibling distance=14mm}]
\node[inner] (root) {$5$}
  child {node[inner] {$3$}
    child {node[inner] {$2$}
      child {node[leaf] {$\ell + 1$}}
      child {node[leaf] {$\ell + 1$}}}
    child {node[leaf] {$\ell$}}}
  child {node[inner] {$2$}
    child {node[leaf] {$\ell$}}
    child {node[leaf] {$\ell$}}};
\node[right=3mm of root, align=left, font=\footnotesize] {size $n = 5\ell + 2$};
\end{tikzpicture}