TREES=$(git cat-file --batch-check='%(objectname) %(objecttype)' --batch-all-objects | grep tree | cut -f1 -d" ")

for TREE in $TREES; do
    if [ "$(git cat-file -p $TREE | wc -l)" -eq 1 ]; then
        if [ "$(git cat-file -p $TREE | cut -f1 | grep tree | wc -l)" -eq 1 ]; then
            # So the tree has exactly one child, and it is a tree!
            TREE2=$(git cat-file -p $TREE | cut -f1 | grep tree | cut -f3 -d" ")
            if [ "$(git cat-file -p $TREE2 | wc -l)" -eq 1 ]; then
                if [ "$(git cat-file -p $TREE2 | cut -f1 | grep tree | wc -l)" -eq 1 ]; then
                    # Same for its child! \o/
                    exit 0
                fi
            fi
        fi
    fi
done

exit 1