在节点下方创建标签（tikz）

Question

我需要在最低顶点的正下方添加标签“b”。

我尝试创建一个附加节点：\node[below] at (-12, -7) {$b$}但是它无法编译（时间耗尽）。

\documentclass[10pt]{article}
\usepackage{amstext}
\usepackage{amsmath}
\usepackage{amsfonts}
\usepackage{amssymb}
\usepackage{amsthm}
\usepackage{array}
\usepackage{tikz}
\usepackage[margin=1.5in]{geometry}    % For reducing margin
\usepackage{graphicx}
\usetikzlibrary{arrows}
\usetikzlibrary{shapes.geometric}
\usetikzlibrary{positioning,arrows.meta,patterns,shadows}
\usetikzlibrary{graphs,graphs.standard,quotes}
\usetikzlibrary{shapes.arrows,patterns}
\usetikzlibrary{positioning,shapes,calc,decorations.pathmorphing}

\begin{document}

\begin{tikzpicture}[scale = 0.5]
\tikzset{% This is the style settings for nodes
    cli/.style={circle,ball color=black,inner sep=0pt,minimum size=5pt],draw, general shadow={fill=gray!60,shadow xshift=1pt,shadow yshift=-1pt}},
    c1/.style={very thick,black}}
\node[cli] (w1) at (-16,-1) {}; 
\node[cli] (w2) at (-14,-3) {};
\node[cli] (w3) at (-12,-6) {};
\node[cli] (w4) at (-10,-3) {};
\node[cli] (w5) at (-8,-1) {};
\draw[c1] (w1) -- (w2);
\draw[c1] (w2) -- (w3);
\draw[c1] (w3) -- (w4);
\draw[c1] (w4) -- (w5);
\draw[c1] (w2) -- (w4); 
\end{tikzpicture}

\end{document}