# Tikz-qtree tree edges that split

I have the following qtree, and cannot figure out why the edges to the leaves start as a single edge then split into two. I am trying to make a binary tree with all the leaves aligned to the bottom, which is why I am setting the distance from root.

\begin{figure}
\begin{minipage}{.6\linewidth}
\begin{tikzpicture}
\tikzset{frontier/.style={distance from root=145pt}}
\Tree [.a
[.b
[.c
[e f ] ]
[.d
[g h ] ] ]
[.i
[.j
[.l
[n o ]]
[.m
[p q ]]]
[.k
[r s ]]]]

\end{tikzpicture}
\end{minipage}\hfill


like this:

with forest is simple:

\documentclass[margin=3mm]{standalone}
\usepackage{forest}

\begin{document}
\begin{forest}
for tree={parent anchor=south,
child anchor=north},
where n children=0{tier=word}{}
[a
[b
[c
[e]
[f]
]
[d
[g]
[h]
]
]
[i
[j
[l
[n]
[o]
]
[m
[p]
[q]
]
]
[k
[r]
[s]
]
]
]
\end{forest}
\end{document}