Recreating a mixed-layout tree diagram

Question

I'm trying to recreate the following diagram from a book:

I tried using tikz's graphdrawing package:

\documentclass{standalone}
\usepackage{tikz} 

\usetikzlibrary {graphs, quotes, graphdrawing} \usegdlibrary{trees}
%\usetikzlibrary {arrows.meta,graphs,graphdrawing} \usegdlibrary {layered}

\begin{document} 
\begin{tikzpicture}
 \graph [
 tree layout, 
% layered layout,
 grow down, branch right, 
 nodes={circle ,draw, minimum size=.65cm, inner sep=0pt, very thick},
 level/.style={
  sibling distance = .15cm,
  sibling sep = 0.25cm,
  level distance = 0cm,
  level sep = 0.1cm  
  }, 
 level 3/.style={
  sibling distance = .0cm,
  sibling sep = 0.6cm,
  level distance = 0cm,
  level sep = 0.1cm  
  }  
 ] {
1--2--{3,4--{6,7},5--{8--{10,11},9}}
 };
\end{tikzpicture}
 
\end{document}

Trying first the tree layout engine:

and then I tried the layered layout engine:

They're pretty close, but neither nails it. The original's layout seems to be a mixture of the two. Notice how the subgraph with 5 as root is layed out as a binary tree, while the 1-2-4 chain is what you get with the layered layout.

I also noticed that in the original, the 4 node sits a tad lower than its siblings. While the use of a different sibling seperation in level 3 in the layered layout places 4 a bit off-center wrt 2 for some reason.

The mammoth tikz manual didn't tell me how to:

1. control level pre distance per node
2. switch between layouts (probably not possible), or
3. alternatively, nudging the leftmost child manually so the rest of the tree aligns properly.

Advice appreciated (including achieving this more easily with something else short of illustrator other than tikz)

Answer 1

If you can consider using forest, this task is rather straightforward. You can just change the calign in the tree. In this example, we can set

for tree={calign child=2}

(or calign=last in this example) in the subtree starting from 4.

\documentclass{article}
\usepackage{forest}
\begin{document}
\begin{forest}
for tree={circle, minimum size=.65cm, inner sep=0pt,draw,thick} 
 [1
  [2
   [3]
   [4,for tree={calign child=2}
    [5]
    [6]
   ]
   [5
    [8
     [10]
     [11]
    ]
    [9]
   ]
  ]
 ]
\end{forest}
\end{document}

Another version with vertically aligned 2 and 4 nodes.

\documentclass{article}
\usepackage{forest}
\begin{document}
\begin{forest}
for tree={circle, minimum size=.65cm, inner sep=0pt,draw,thick} 
 [1
  [2
   [3]
   [4,for tree={calign child=2},for current={calign with current edge}
    [5]
    [6]
   ]
   [5
    [8
     [10]
     [11]
    ]
    [9]
   ]
  ]
 ]
\end{forest}
\end{document}

Answer 2

Thanks to @user238301's suggestion to use the forest package, I was able to recreate the exact layout.

Note the details of the original layout:

• 2 but must be centered between 3 and 5
• 4-7 must be aligned directly below 1-2
• 6 and 7 must be "pushed" left so 7 is below 4, while 8 and 9 must be placed symmetrically about 5 (and below)

Getting this right was harder than expected.

Here's the reproduction and the original side-by-side (which is which? :-) ):

And here's the code:

\documentclass{article} 
\usepackage{forest} 
\begin{document} 
\begin{forest}
for tree={circle, minimum size=.65cm, inner sep=0pt,draw, very thick,edge={line width=1.5pt}}
 [1,for tree={l sep=0.15cm, l=0cm}
  [2,calign=center, for tree={l sep=0.05cm, s sep=0.3cm}
   [3]
   [4, before computing xy={s=0mm},for tree={calign=last, s sep=0.05cm}
    [6]
    [7]
   ]
   [5,for tree={calign=center, s sep=0.05cm}
    [8
     [10]
     [11]
    ]
    [9]
   ]
  ]
 ]
\end{forest}
\end{document}
\end{document}