\resizebox{1\columnwidth}{!}{%
  \begin{tikzpicture}[%
    ns/.style = {
      draw=none,
    },
    ps/.style = {
      draw,
      -latex,
    },
  ]
    \node[ns](gossip){};
    \node[ns,right=0pt of gossip](retroactive){\textbf{Retroactive}};
    \node[ns,left=0pt of gossip](proactive){\textbf{Proactive}};

    % proactive
    \node[ns,left=12pt of proactive](cross){STH cross-logging~\cite{minimal-gossip,ietf-cross-logging,hof-cross-logging,catena}};
    \node[ns,above=0pt of cross](push){STH pushing~\cite{google-gossip}};
    \node[ns,below=0pt of cross](cosi){STH cosigning~\cite{cosi}};

    \path[ps] (proactive) -- (push.east);
    \path[ps] (proactive) -- (cross);
    \path[ps] (proactive) -- (cosi.east);

    % retroactive
    \node[ns,right=12pt of retroactive](implicit){Implicit via multipath~\cite{mpaudit}};
    \node[ns,above=0pt of implicit](pool){STH pooling~\cite{chuat-gossip,ietf-gossip}};
    \node[ns,below=0pt of implicit](trust){Trusted auditing~\cite{ietf-gossip}};
    \node[ns,above=14pt of retroactive.north east](feedback){SCT feedback~\cite{ietf-gossip}};
    \node[ns,below=14pt of retroactive.south east](bee){CT honey bee~\cite{ct-honey-bee}};

    \path[ps] (retroactive) -- (feedback);
    \path[ps] (retroactive) -- (pool.west);
    \path[ps] (retroactive) -- (implicit);
    \path[ps] (retroactive) -- (trust.west);
    \path[ps] (retroactive) -- (bee);
  \end{tikzpicture}
}