​@connecter interesting case. I have the feeling that the points shown below with the red circles is the most challenging part:

It would nice to exclude them when your NeigbhourFinder + VertexCreator run. Is that possible?
If so, than you could include these challenge points in a second run and then connect them to the already created blue lines as you showed in the Goal image.

Hi ​@lambertus and thank you for your answer. The area shown is of course only an example and there are many more points. What makes it particularly difficult, of course, is that it depends very much on which point is taken first and which is taken last. 
If, for example, a point further south towards the route had been taken first, the result would look like this:

But that's okay, the main thing is that not all of them are simply connected to the start line layer.

​@connecter thanks for your reply, I have an idea how this could be solved. Will make some sample data and build a workspace. I will keep you posted.

Considering 2 cases seems to be the great way, simple line with a unique point and “complex ones” with several points. Your “complex geometry is based on a simple line (in blue) in which other points are connected to. If you choose the highest point (in red) you will have the line that have to be connected to other points (in green), but if the configuration is not always like this, it’s probably something else.

A possible starting point would be to create perpendicular ‘segments’ (polygons) that extend out from line. You can then use these to ‘group’ the points. In each group, you can then figure out which point is furthest, and use that for the ‘trunk’ line. Then for each other point in the group determine if you want to snap that ‘trunk’ to the vertex, or add a branch connecting the point to the branch.

If I have some time later in the day/week, I can expand a bit on this