gnus-subscribe-hierarchical-interactive

gnus-subscribe-hierarchical-interactive is a variable defined in `gnus-start.el'.
Its value is

nil

Documentation:
*If non-nil, Gnus will offer to subscribe hierarchically.
When a new hierarchy appears, Gnus will ask the user:

'alt.binaries': Do you want to subscribe to this hierarchy? ([d]ys):

If the user pressed `d', Gnus will descend the hierarchy, `y' will
subscribe to all newsgroups in the hierarchy and `s' will skip this
hierarchy in its entirety.

You can customize this variable.