How does one use \node[inner node]{}?

Question

I'm trying to reproduce a TikZ tree from a Till Tantau presentation (see pg.33 of this .pdf)

My code is as follows:

    \documentclass{article}

    \usepackage[latin1]{inputenc}
    \usepackage{tikz}
    \usetikzlibrary{trees}
    \begin{document}

    \begin{tikzpicture}[edge from parent fork down, edge from parent/.style={black,thick,draw}]

    \node[inner node]{}
        child { node {bacteria} }
        child {  node[inner node] {}
            child { node {plants} }
            child   { node[inner node] {}
                child { node[inner node] {}
                    child { node {fish} }
                    child { node[inner node] {}
                        child { node {mammals} }
                        child { node {birds} }
                    }
                }
                child { node[inner node] {}
                    child { node {dragonflies} }
                    child { node {beetles} }
                }
            }               
        };

    \end{tikzpicture}

    \end{document}

I get six errors of the type below for each of the six node[inner node] {} calls in the code above:

    ! Package pgfkeys Error: I do not know the key '/tikz/inner node' and I am goin
    g to ignore it. Perhaps you misspelled it.
    See the pgfkeys package documentation for explanation.
    Type H <return> for immediate help.
    ...
    l.11 \node[inner node]
    {}
    This error message was generated by an \errmessage
    command, so I can't give any explicit help.
    Pretend that you're Hercule Poirot: Examine all clues,
    and deduce the truth by order and method.

I couldn't find anyting pertinent on this type of usage in the PGF manual. Any help is welcome!

Answer 1

I think that the presentation of Till Tantau does not really define the inner node style. I have the impression that he just wanted to illustrate that one can provide "some kind of options".

You can write

\begin{tikzpicture}[....,inner node/.style={fill,black,circle}]

to define it somehow. I tried to reproduce some filled dot, try out if this is what you want. If not, you may want to experiment with out tikz options.