Like @निरंजन already said, don't leave empty lines in trees.
Besides this I suggest:
- to use `sloped` for the labels to make them easier to read
- increase the vertical distance with `l sep` to get a bit more space to place the labels
- manually adding a couple of phantom notes to get more homogeneous spacing in the second row
```
\documentclass{standalone}
\usepackage{forest}
\tikzset{mylabel/.style={midway,font=\tiny,above,sloped}}
\begin{document}
\begin{forest}
%label tree,
for tree={
circle,
draw,
edge+=thick,
l sep=10mm,
minimum width=2em,
minimum height=2em,
inner sep=0pt,
font=\strut\footnotesize\sffamily,
},
[root
[10,edge label={node[mylabel,very near end]{(10,10)}}]
[,phantom]
[0,edge label={node[mylabel,near end]{(0,10)}}]
[,phantom]
[,edge label={node[mylabel,near end]{(9,9)}}
[9, edge label={node[mylabel]{(10,10)}}]
[, edge label={node[mylabel]{(6,6)}}
[8, edge label={node[mylabel]{(10,10)}}]
[5, edge label={node[mylabel]{(7,10)}}]
]
[6, edge label={node[mylabel]{(7,10)}}]
]
[,edge label={node[mylabel,near end]{(3,3)}}
[4, edge label={node[mylabel]{(5,10)}}]
[3, edge label={node[mylabel]{(4,10)}}]
]
[,edge label={node[mylabel,near end]{(2,2)}}
[2, edge label={node[mylabel]{(3,10)}}]
[1, edge label={node[mylabel]{(2,10)}}]
]
[,phantom]
[7,rectangle,edge label={node[mylabel,very near end]{(7,10)}}]
]
\end{forest}
\end{document}
```
![document.png](/image?hash=bd571493e9504bb7b1f4d95d650f0a8692fa453a8108e329e68dc55a618bab7b)