Some say that the Catholic Church is one.
Now, this is fun! If it can be said that the Catholic Church has had thousands of spin-off denominations, then it could be claimed that the Orthodox had ALL of them --- if you see it as Orthodox --> Catholic --> All the other (let's agree on a figure: bajillion) Christian denominations.
But if you ask all the other denominations whether they are spun-off Catholics (or Orthodox), I'll wager most of them would say, "No."
And if you ask Catholics if they are spun-off from the Orthodox, they'll say "No," beinst they both were the same original church for 1000 years, and the Catholics still recognize every one of the Orthodox sacraments, seeing the Orthodox not as heretics but simply true and valid Churches in schism.
If you ask the Orthodox if they are spun-off from the Catholics, they'll say "No," and (many, but not all) would say moreover that the Catholics are heretical.
And the Catholics recognize ALL Christian Trinitarian baptisms (excluding only Mormon because they are not, properly speaking, Trinitarian), saying that Baptism makes one a member of the Church, and therefore all baptized Christians are certainly, though imperfectly, Catholic.
Meanwhile, the Orthodox don't necessarily recognize all Baptisms, not even of other Orthodox.
To illustrate: my dear husband Don-o was baptized a Baptist when he was an adolescent, and this Baptism was recognized by the Catholic Church, which gave him the right (as a validly baptized person)to marry Sacramentally in the Catholic Church. But when he became an Antiochian Orthodox, they Baptized him again, and then when he switched to ROCOR (Russian Orthodox Church Outside of Russia) he was baptized yet again! (The Dunkard!)
So the Catholics seem most "catholic," Baptism-wise, in respect of which there are no denominational divisions.
So welcome, Alex and GoLightly, fellow Catholics!
(I mean that in manner half-jesting and entirely--- entirely --- sincere.)