Comme ça?
\documentclass[a4paper,12pt,DIV50]{article}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage{lmodern}
\usepackage{graphicx}
\usepackage[french]{babel}
\usepackage[]{tikz}
\usetikzlibrary{shapes}
\begin{document}
\begin{tikzpicture}
\begin{scope}[local bounding box=foo]
\draw (1,0) node {$A$} (5,0) node{$B$} (10,0) node {$C$};
\end{scope}
\draw (foo.south west) rectangle (foo.north east);
\end{tikzpicture}
\end{document}
![alt text][1]
-----
Utilisation pour plus d'éléments :
\documentclass[a4paper,12pt,
%DIV50
]{article}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage{lmodern}
\usepackage{graphicx}
\usepackage[french]{babel}
\usepackage[]{tikz}
\usetikzlibrary{shapes}
\begin{document}
\begin{tikzpicture}
\begin{scope}[local bounding box=foo]
\draw (1,0) node {$A$} (5,0) node{$B$} (10,0) node {$C$};
\end{scope}
\draw (foo.south west) rectangle (foo.north east);
\node (zzz) at (8,-5) {D};
\draw[->] (foo.south) |- (zzz);
\end{tikzpicture}
\end{document}
![alt text][2]
---
\documentclass[a4paper,12pt,
%DIV50
]{article}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage{lmodern}
\usepackage{graphicx}
\usepackage[french]{babel}
\usepackage[]{tikz}
\usetikzlibrary{shapes,positioning}
\begin{document}
\begin{tikzpicture}
\begin{scope}[local bounding box=foo]
\node (A) at (1,0) {$A$};
\node (B) at (5,0) {$B$};
\node (C) at (10,0) {$C$};
\end{scope}
\draw (foo.south west) rectangle (foo.north east);
\node[below of = A,node distance=3cm] (A1) {A1};
\node[below of = B,node distance=3cm] (B1) {B1};
\node[below of = C,node distance=3cm] (C1) {C1};
\draw[->] (A.south) -- (A1);
\draw[->] (B.south) -- (B1);
\draw[->] (C.south) -- (C1);
\end{tikzpicture}
\end{document}
![alt text][3]
[1]: https://texnique.fr/osqa/upfiles/Screen_Shot_2019-07-08_at_19.06.32.png
[2]: https://texnique.fr/osqa/upfiles/Screen_Shot_2019-07-08_at_19.07.24.pnghttps://texnique.fr/osqa/upfiles/Screen_Shot_2019-07-08_at_19.07.24.png
[3]: https://texnique.fr/osqa/upfiles/Screen_Shot_2019-07-08_at_19.23.00.png
