How do I create a Tikz mindmap that has two connected roots?

Question

I am creating a mindmap that has multiple root concepts instead of just one. How can I create such a mindmap using Tikz?

These are the mindmaps:

\begin{tikzpicture}[small mindmap,concept color=brown!30]
\node (right) at (2,0) [concept] {Right}
  [clockwise from=70]
  child { node[concept] {R.1} }
  child { node[concept] {R.2} }
;
\node (left) at (-2,0) [concept] {Left}
  [counterclockwise from=210]
  child { node[concept] {L.1}  }
  child { node[concept] {L.2} }
;
\end{tikzpicture} 

Looking like this:

It would be nice if they were of different color and the connecting line a gradient matching those colors.

Answer 1

Section 39.4.3 of the Tikz manual helped me to get a clean solution in which two root nodes can be directly connected using a circle connection bar path:

\documentclass[landscape]{article}
\usepackage{tikz}
\usetikzlibrary{mindmap}
\pagestyle{empty}
\begin{document}
\begin{tikzpicture}[small mindmap, outer sep=0pt, text=black]

\begin{scope}[concept color=brown!30]
\node (right) at (2,0) [concept] {Right}
  [clockwise from=70]
  child { node[concept] {R.1} }
  child { node[concept] {R.2} }
;
\end{scope}

\begin{scope}[concept color=green!40!black!30]
\node (left) at (-2,0) [concept] {Left}
  [counterclockwise from=210]
  child { node[concept] {L.1}  }
  child { node[concept] {L.2} }
;
\end{scope}

\path (left) to[circle connection bar switch color=from (green!40!black!30) to (brown!30)] (right) ;

\end{tikzpicture}
\end{document}

Resulting in:

The scopes look somewhat tricky but I needed those to get the fill colors right.