The same is true in this case. There was a Christianity of the second-century, but it wasn't what scholars generally call "normative" Christianity (by which they mean, apostolic or mainstream). Again, what a person considered "normative" Christianity in the second century was whatever expression of Christianity that person followed. No one expression of Christianity controlled the landscape, although many were battling to do so and consolidating power in the process. So there was variety, there were Christianities.
But to say this doesn't mean there wasn't "Christianity." Indeed, there was. It took its shape from several issues such as christology, communal practices like baptism and eucharist, methods of interpretation of scripture, relevance of Jewish scripture, sacralization of Christian scriptures, worship days, leadership and liturgical calendars. All the forms of Christianity in the second century were part of this web of religiosity, a religiosity that was consolidating in terms of the formation of Christian self-identity as something separate from (even against) Judaism and paganism.
So once again I continue to talk about "Christianity" in the second century, even though I recognize that this took on a variety of expressions. Here is an excerpt from The Thirteenth Apostle where I try to talk about this very issue:
The purpose of the Gospel of Judas was to criticize "mainstream" or "apostolic" Christianity from the point of view of the Sethian Gnostics. The Sethian Christians, whose religious beliefs I will describe in detail in the next chapter, were involved in an intra-religious debate that was raging in the second century as a number of distinct Christianities struggled for control of Christianity. Christianity in the second century was not controlled by a single church or a single hierarchy or a single orthodoxy. In fact, "orthodoxy" (correct thinking and practice) and "heresy" (wrong thinking and practice) were very relative terms. Who was orthodox and who was a heretice depended upon where you were standing. If you were a mainstream or apostolic Christian, you were orthodox and everyone else was a heretic. If you were a Sethian Gnostic Christian, you were orthodox and everyone else was a heretic (p. 5).