\begin{forest}
for tree={
math content,
grow'=0,
calign primary child=1,
calign primary angle=-30,
calign=last,
delay={
if iteration={}{iteration/.option=level, is auto iteration}{},
},
},
this edge label/.style 2 args={% #1 = additional node options, #2 = denominator
edge label={node [midway, anchor=south east, xshift=-2.5pt, font=\scriptsize, #1] {$\frac{2}{#2}$}}
},
parent edge label/.style 2 args={% #1 = numerator, #2 = denominator
!u.edge label={node [midway, below, font=\scriptsize] {$\frac{#1}{#2}$}},