Loft between lines

Good morning, I am trying to join with a loft of lines but it does not join them, I am trying various ways but there is nothing to do as it does not connect the lines in “vertical”.

I even thought about extruding the lines and then trimming with “Surface trim” everything above the lines but I don’t know how to do it.

Plugging two wires into one input is generally a bad idea - keep your data structure clean, don’t let it act on assumptions - try this:
(If your trees have different paths, you might also want to Simplify Paths as well as Grafting them)