gnus-thread-hide-subtree

gnus-thread-hide-subtree is a variable defined in `gnus-sum.el'.
Its value is

nil

Documentation:
*If non-nil, hide all threads initially.
This can be a predicate specifier which says which threads to hide.
If threads are hidden, you have to run the command
`gnus-summary-show-thread' by hand or select an article.

You can customize this variable.