Consider the MWE (copied from here):
\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}
Now I want that, R.1 and L.1 will be merged to a single node. In other words, the two root nodes will share a common child. Any advice will be appreciated.
EDIT
The linked question asks the same problem. However, I would like to point out that the accepted answer to this question does not (in my humble understanding) solve the problem. It intelligently places one child on top of another, creating an impression that a child is shared. Apparently, it needs manual processing to place the node in the middle (which can be tedious, as can be seen from the other answer).
clockwise from=70), so that would not be a big difference I think? Change 70 into 150 or so and see how it looks. – Marijn Jun 06 '19 at 16:28\node (left) at (-2,0)not manual? Or are you asking if one can compute the relevant shift from pgf keys? This is of course possible. – Jun 06 '19 at 16:32