Binary Search Tree

\usepackage{forest}

\begin{forest}
  for tree={circle, draw, minimum size=2em, inner sep=1pt, s sep=10mm}
  [8
    [3
      [1]
      [6
        [4]
        [7]
      ]
    ]
    [10
      [{}]
      [14
        [13]
        [{}]
      ]
    ]
  ]
\end{forest}