Matthew 7:17 - Even so, every good tree bears good fruit, but a bad tree bears bad fruit. 18 A good tree cannot bear bad fruit, nor can a bad tree bear good fruit. 19 Every tree that does not bear good fruit is cut down and thrown into the fire. Do "bad" trees which "do not bear good fruit" represent believers? NO. What happens to them? They are cut down and thrown into the fire. It's the same in John 15:6.Unfortunately Jesus is speaking here of bearing fruit, as He usually did in all His teachings.
For instance, even in Mathew 7:19.
John 15:5-6 New American Standard Bible (NASB)
5 I am the vine, you are the branches; he who abides in Me *(like the 11 remaining disciples)* and I in him, he bears much fruit, for apart from Me you can do nothing.
6 If anyone does not abide in Me, *(like Judas Iscariot)* he is thrown away as a branch and dries up; and they gather them, and cast them into the fire and they are burned.