what does second て mean after て-form?


There is a phrase said by a native speaker in a video and the subtitles (not
autogenerated) were:

そんなゴミの中で **寝てて** 快適なの。

I cannot find what does this second て mean. The form 寝て must refer to
continuous action, but then before the 快適 adjective there is one more て. What
is the meaning and the name for this construction?

