\node[draw,circle,label=below:{$\mathrm{base}$},fill,outer sep=0.1cm, inner sep=0pt, minimum size=0.1cm] (a0) at (0, -1) {};
\draw[->] (0, 0) circle (1cm);
\node[] (loop) at (0, 0) {$\mathrm{loop}\ i$};