\documentclass[tikz]{standalone}
\usepackage{tikz}
\usetikzlibrary{trees}

\begin{document}
\begin{tikzpicture}[
  level 1/.style={sibling distance=80mm},
  level 2/.style={sibling distance=40mm},
  level 3/.style={sibling distance=20mm},
  level 4/.style={sibling distance=10mm},
  every node/.style={
    circle,
    draw=blue,
    fill=blue!20,
    minimum size=6mm
  }
]
\node {0}
  child {node {1}
    child {node {3}
      child {node {7}
        child {node {15}}
        child {node {16}}
      }
      child {node {8}
        child {node {17}}
        child {node {18}}
      }
    }
    child {node {4}
      child {node {9}
        child {node {19}}
        child {node {20}}
      }
      child {node {10}
        child {node {21}}
        child {node {22}}
      }
    }
  }
  child {node {2}
    child {node {5}
      child {node {11}
        child {node {23}}
        child {node {24}}
      }
      child {node {12}
        child {node {25}}
        child {node {26}}
      }
    }
    child {node {6}
      child {node {13}
        child {node {27}}
        child {node {28}}
      }
      child {node {14}
        child {node {29}}
        child {node {30}}
      }
    }
  };
\end{tikzpicture}
\end{document}