After a while I found a good way to do it.
Only problem is the fact that the color is gray for some reason and when you move your camera above it it turns black.
node = scene_->CreateChild("Triangle");
ur::CustomGeometry *geometry = node->CreateComponent<ur::CustomGeometry>();
geometry->BeginGeometry(0, ur::TRIANGLE_LIST);
geometry->DefineVertex({ 0,0,0 });
geometry->DefineTexCoord({ 1,0 });
geometry->DefineColor({ 255,0,0 });
geometry->DefineVertex({ 10,0,0 });
geometry->DefineTexCoord({ 0,1 });
geometry->DefineColor({ 255,0,0 });
geometry->DefineVertex({ 10,10,0 });
geometry->DefineTexCoord({ 0,0 });
geometry->DefineColor({ 255,0,0 });
geometry->Commit();
After I did that, voila! It loads! http://prntscr.com/fckn0w
Don’t know how to fix the colors though