Eliminate distance from phantom node in forest

Question

Ignasi's answer to Forest trees on the same line shows how to effectively draw two trees in the same forest environment using the phantom trick noted in the forest documentation.

Doing this, however, leads to extra vertical distance in the tree(s), which is quite noticeable when aligned with something else. For example, putting the trees inside of an \ex leads to the "top" of the trees starting below the example number.

Is there a way to eliminate this extra distance so that the "tops" of the two trees are aligned with the example number?

MWE

\documentclass{article}

\usepackage{forest}
\usepackage{gb4e}

\begin{document}

\begin{exe}
    \ex{
        \begin{forest} baseline
            [, phantom, s sep = 3em
                [asdf
                    [a]
                    [b]
                ]
                [asdf
                    [a]
                    [b]
                ]
            ]
        \end{forest}
    }
\end{exe}

\end{document}

Answer 1

Maybe I've misunderstood but could you not do something like this?

\documentclass{article}

\usepackage{forest}
\usepackage{gb4e}

\begin{document}

\begin{exe}
    \ex{
        \begin{forest}
          for tree={
            where level=0{
              for children={%
                l sep=0pt,
                baseline},
            }{},
          },
            [, phantom, s sep = 3em
                [asdf
                    [a]
                    [b]
                ]
                [asdf
                    [a]
                    [b]
                ]
            ]
        \end{forest}
    }
\end{exe}

\end{document}