\begin{figure}[h]
\centering
\begin{tikzpicture}[level/.style={sibling distance=35mm/#1},style={>=latex,->}]
    \tikzstyle{every node}=[circle,draw,text centered,minimum height=2.5em]
    \node[tree,draw=red] (z) {}
        child {
            node[tree] {}
            child { node[tree] {\Large $a$} }
            child { node[tree] {\Large $b$} }
        }
        child {
            node[tree] {}
            child { node[tree] {\Large $c$} }
        }
        child {
            node[tree,draw=red] (1) {}
            child { node[tree] {\Large $d$} }
            child {
                node[tree,draw=red] (2) {}
                child { node[tree,draw=red] (3) {\Large $e$} }
                child { node[tree] {\Large $f$} }
            }
        }
    ;

    \path[-latex,color=red] (z) edge[bend left=20] (1);
    \path[-latex,color=red] (1) edge[bend left=20] (2);
    \path[-latex,color=red] (2) edge[bend right=20] (3);
\end{tikzpicture}
\caption{Пример дерева с отмеченным путем от корня к листу}
\label{fig:simple-tree}
\end{figure}