Forest tree with labelled edges and no nodes on the ends

Question

... one upon the time ... :) I draw this tree

by CorelDraw! for presenting convolution coding rules, which I like now to redraw and modernize with help of forest package. I stuck at followings:

• skip drawing nodes on the end of tree
• placings edge labels on better/shorter way
• make tree layout symmetrical at all tree levels

I kindly ask help me in the following to resolve above listed problems as well to add names to nodes in tree for later use, for example draw input line with condition for branching, for append some legend and auxiliary images or for callout nodes (balloons) for some explanations.

So far I manage to write the following code:

\documentclass[tikz,
               margin=3mm,
               preview]{standalone}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}

\usepackage{forest}
%---------------------------------------------------------------%
    \begin{document}
   \begin{forest}
    for tree={% style of tree nodes
      circle, font=\small\sffamily,
             fill = blue!60!black,
     minimum size = 4mm, 
        inner sep = 0.5pt,
             text = white,
              % style of tree (edges, distances, direction)
             edge = {draw, semithick},
  edge path={
    \noexpand\path[\forestoption{edge}]
      (!u.parent anchor) |-
      (.child anchor) -- % intermediate point
      (.child anchor)\forestoption{edge label};
  },
             grow = east,
            s sep = 2mm,    % sibling distance
            l sep = 12mm,   % level distance
               }
[a
    [b,edge label={node[xshift=-9mm,fill=white]{11}}
        [d,edge label={node[xshift=-9mm,fill=white]{01}}
            [d,edge label={node[xshift=-9mm,fill=white]{10}}
                [,edge label={node[xshift=-9mm,fill=white]{10}}]
                [,edge label={node[xshift=-9mm,fill=white]{01}}]
            ]
            [c,edge label={node[xshift=-9mm,fill=white]{01}}
                [,edge label={node[xshift=-9mm,fill=white]{00}}]
                [,edge label={node[xshift=-9mm,fill=white]{11}}]
            ]
        ]
        [c,edge label={node[xshift=-9mm,fill=white]{10}}
            [b,edge label={node[xshift=-9mm,fill=white]{00}}
                [,edge label={node[xshift=-9mm,fill=white]{10}}]
                [,edge label={node[xshift=-9mm,fill=white]{01}}]
            ]
            [a,edge label={node[xshift=-9mm,fill=white]{11}}
                [,edge label={node[xshift=-9mm,fill=white]{11}}]
                [,edge label={node[xshift=-9mm,fill=white]{00}}]
            ]
        ]
    ]
    [a,edge label={node[xshift=-9mm,fill=white]{00}}
        [b,edge label={node[xshift=-9mm,fill=white]{11}}
            [d,edge label={node[xshift=-9mm,fill=white]{01}}
                [,edge label={node[xshift=-9mm,fill=white]{10}}]
                [,edge label={node[xshift=-9mm,fill=white]{01}}]
            ]
            [c,edge label={node[xshift=-9mm,fill=white]{10}}
                [,edge label={node[xshift=-9mm,fill=white]{00}}]
                [,edge label={node[xshift=-9mm,fill=white]{11}}]
            ]
        ]
        [a,edge label={node[xshift=-9mm,fill=white]{00}}
            [b,edge label={node[xshift=-9mm,fill=white]{11}}
                [,edge label={node[xshift=-9mm,fill=white]{01}}]
                [,edge label={node[xshift=-9mm,fill=white]{10}}]
            ]
            [a,edge label={node[xshift=-9mm,fill=white]{00}}
                [,edge label={node[xshift=-9mm,fill=white]{11}}]
                [,edge label={node[xshift=-9mm,fill=white]{00}}]
            ]
        ]
    ]
];
    \end{forest}
\end{document}

Answer 1

Hard to say about the labelling without knowing what it should look like. You can define a variable to hold it and use that, define a style or use one of various automated-labelling options, if there's a pattern.

The rest is fairly straightforward, I think.

• Distinguish terminal nodes from the others by testing to see if they have any children.

• Use name to name a node for later reference.

• Use invisible terminal nodes for spacing and symmetry.

\documentclass[border=10pt,multi,tikz]{standalone}
\usepackage{forest}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\forestset{
  declare toks={way label}{},
}
\begin{document}
\begin{forest}
  for tree={% style of tree nodes
    semithick,
    font=\small\sffamily,
    edge = {draw, semithick},
    grow = 0,
    s sep = 2mm,    % minimum sibling distance
    l sep = 12mm,   % minimum level distance
    edge path'={
      (!u) |- (.child anchor)\forestoption{edge label}
    },
    circle,
    minimum size=4mm,
    inner sep=.5pt,
    anchor=center,
  },
  where n children=0{}{
    draw,
    fill = blue!60!black,
    text = white,
  },
  before typesetting nodes={
    where way label={}{}{
      edge label={
        node [pos=.75, fill=white, font=\sffamily] {\forestoption{way label}}
      },
    },
  }
  [a
    [b, way label=11
      [d
        [d
          []
          []
        ]
        [c
          []
          []
        ]
      ]
      [c
        [b
          []
          []
        ]
        [a
          []
          []
        ]
      ]
    ]
    [a
      [b
        [d, name=zarko
          []
          []
        ]
        [c
          []
          []
        ]
      ]
      [a
        [b
          []
          []
        ]
        [a, name=bob
          [, way label=11
          ]
          [, for current and ancestors={way label=00}
          ]
        ]
      ]
    ]
  ]
  \draw [<->, shorten >=20pt, shorten <=20pt] (zarko) -- (current bounding box.east |- zarko) -- ++(5pt,0) |- (bob);
\end{forest}
\end{document}