I believe the verse you are referring to is verse 12 of Jude. In Jude 12 and 23, Jude presents six metaphors taken from nature to describe the false brethren who have come in secretly into the fellowship of believers. They are described as:

12) These are sunken rocks in your love feasts, feasting together fearlessly, pasturing themselves; clouds without water, being carried around by the winds, autumnal trees, without fruit, having died twice, having been rooted up;

13) raging waves of the sea, foaming their own shames; wandering stars, for whom the gloom of darkness has been reserved forever.

The phrase in question is, "autumnal trees, without fruit, having died twice, having been rooted up." This metaphor is describing them as trees that were made to bear fruit in autumn. Not only have they not borne fruit as they were meant to do, but also have been rooted up. This is described as, "having died twice" - dead to bearing fruit and dead in their roots.