The original church is Jews who believed in Jesus. Jesus is the root, and Jews are the original branches. Many of the original branches were broken off so that you- a wild olive shoot- could be grafted in. All Gentiles belong to branches that have been grafted onto someone else’s tree. It’s described in Romans 11.
"Now I am speaking to you Gentiles. Inasmuch then as I am an apostle to the Gentiles, I magnify my ministry 14 in order somehow to make my fellow Jews jealous, and thus save some of them. 15 For if their rejection means the reconciliation of the world, what will their acceptance mean but life from the dead? 16 If the dough offered as firstfruits is holy, so is the whole lump, and if the root is holy, so are the branches.
17But if some of the branches were broken off, and you, although a wild olive shoot, were grafted in among the others and now share in the nourishing root of the olive tree, 18 do not be arrogant toward the branches. If you are, remember it is not you who support the root, but the root that supports you. 19 Then you will say, “Branches were broken off so that I might be grafted in.” 20 That is true. They were broken off because of their unbelief, but you stand fast through faith. So do not become proud, but fear. 21 For if God did not spare the natural branches, neither will he spare you. 22 Note then the kindness and the severity of God: severity toward those who have fallen, but God’s kindness to you, provided you continue in his kindness. Otherwise you too will be cut off. 23 And even they, if they do not continue in their unbelief, will be grafted in, for God has the power to graft them in again. 24 For if you were cut from what is by nature a wild olive tree, and grafted, contrary to nature, into a cultivated olive tree, how much more will these, the natural branches, be grafted back into their own olive tree.
Whose olive tree is it? Who are the original branches? Not you, son. Let me remind you who this letter was written to specifically: ROME! This is YOUR letter. It’s telling the Church in Rome that THIS ISN’T YOUR OLIVE TREE. You were grafted in along with many other branches, and you are NOT the original branches- the original branches are identified, and get this: IT ISN’T YOU. So if you don’t mind, you can stop referring to those “different” branches as separate churches and start referring to them as “other” branches who, like you, share in the same nourishing root of the olive tree. God is not the author of confusion, but you only said that in order to throw up a straw man and beat it right back down. God’s Church is a tree with many branches that have been grafted in, and you are one of them. That isn’t too confusing, is it? It’s explained right there in the letter TO ROME.