Use your wide-open CA test shot, and examine the branches. If they have a translucent look, it’s probably due to halation. (Colours Magazine)

Halation creates secondary ghost images in the film, which to photographers is bad because they are a by-product of unintentional light and film interaction. (anbstudio)

To combat halation, film manufacturers treat the base of the film to reduce or nullify reflections. Grey base is a film base permanently dyed a low density grey colour, this reduces reflection back into the emulsion and light-piping within the base. (National Film and Sound Archive)