# How to write a tree with no (visible) root with TikZ?

I’m trying to write a tree structure in TikZ. The trees in question are labelled on the leaf only; there is no label on inner nodes. Because I don’t use node on inner nodes, the tree structure joins. However, it seems I still need to write a \node to start the tree. While I can leave its label empty, it is still displayed as a white circle which disconnect the structure. How can I avoid this?

\documentclass{article}
\usepackage{tikz}

\begin{document}

% The broken structure bothers me
\begin{tikzpicture}
\node {}
child { node {a} }
child {
child {node {b}}
child {node {c}}
}
;
\end{tikzpicture}

% This is what I want, but without the added root.
\begin{tikzpicture}
\node {} % this node should not exist
child {
child { node {a} }
child {
child {node {b}}
child {node {c}}
}
}
;
\end{tikzpicture}

\end{document}

-

I assume this is what you want:

\begin{tikzpicture}
\coordinate
child { node {a} }
child {
child {node {b}}
child {node {c}}
}
;
\end{tikzpicture}


-