\tikzset{
  treenode/.style = {align=center, inner sep=0pt, text centered, font=\sffamily},
  node_split/.style = {treenode, circle,inner sep=1pt, white, font=\sffamily\bfseries, draw=black, fill=black},
  node_cu/.style = {treenode, circle, draw, thick, font=\sffamily\bfseries\scriptsize, text width=.95em}
}

\begin{tikzpicture}[->,>=stealth',
  level 1/.style={level distance = 1.4cm, sibling distance=1.65cm},
  level 2/.style={level distance = 1.4cm, sibling distance=.85cm},
  level 3/.style={level distance = 1.4cm, sibling distance=.55cm},
]

\node [node_split] {}
child{ node [node_split] {}
  child{ node [node_cu] {1} }
  child{ node [node_split] {}
    child{ node [node_cu] {2} }
    child{ node [node_cu] {3} }
    child{ node [node_cu] {4} }
    child{ node [node_cu] {5} }
  }
  child{ node [node_cu] {5} }
  child{ node [node_cu] {6} }
}
child{ node [node_cu] {7} }
child{ node [node_split] {}
  child{ node [node_cu] {8} }
  child{ node [node_split] {}
    child{ node [node_cu] {9} }
    child{ node [node_cu] {10} }
    child{ node [node_cu] {11} }
    child{ node [node_cu] {12} }
  }
  child{ node [node_cu] {13} }
  child{ node [node_cu] {14} }
}
child{ node [node_cu] {15} }
;
\end{tikzpicture}