# Tree diagram has lopsided branch

I'm attempting to draw a tree diagram using the forest package that shows the morphological derivation of a word. However, when I align the terminal nodes, the highest branch looks lopsided. This is what I have:

\usepackage[linguistics]{forest}

\begin{forest}
[un, tier=morph]
[lock, tier=morph]
[able, tier=morph]
]
]
\end{forest}


This produces the following:

How might I increase the height of the top node or set it further to the right so that all the branches split at the same angle?

You can ask for fixed angles or fixed edge angles.

\documentclass{article}
\usepackage[linguistics]{forest}
\begin{document}
\begin{forest}
for tree={calign=fixed angles}
[un, tier=morph]
[lock, tier=morph]
[able, tier=morph]
]
]
\end{forest}

\begin{forest}
for tree={calign=fixed edge angles}
[un, tier=morph]
[lock, tier=morph]
[able, tier=morph]
]
]
\end{forest}
\end{document}


I'm not a linguist, just a marmot, and I would do

\documentclass{article}
\usepackage{forest}
\begin{document}
\begin{forest}
for tree={calign=fixed angles,parent anchor=south}
[un, tier=morph]
[lock, tier=morph]
[able, tier=morph]
]
]
\end{forest}

\begin{forest}
for tree={calign=fixed edge angles,parent anchor=south}