How to order a list of numbers without changing the list

I am in need of ordering a list of numbers stored in a C++ vector:

#include <vector>
#include <iostream>


struct Oid
{
    Oid(std::vector<oid_data_unit> _oid_) : mOid(_oid_) {}
    Oid(std::initializer_list<oid_data_unit> _oid_) : mOid(_oid_) {}
    std::vector<oid_data_unit> mOid;
};

bool compare(Oid i1, Oid i2) 
{ 
    if(i1.size() > i2.size())
        return true;; 
}  

int main()
{
Oid  e({ 1, 3, 6, 1, 2, 1, 2,2,1, 4 })
Oid  c({ 1, 3, 6, 1, 2, 1, 2, 2, 3 });
Oid  b({ 1, 3, 6, 1, 2, 1, 2, 1, 0 });
Oid  a({ 1, 3, 6, 1, 2, 1, 2 });
Oid  d({ 1, 3, 6, 1, 2, 1, 2,2,1, 3 });
std::vector<Oid> ax;
ax.emplace_back(a);
ax.emplace_back(b);
ax.emplace_back(c);
ax.emplace_back(d);
ax.emplace_back(e);
std::sort(ax.begin(), ax.end(), compare); 
return 0;
}

As per the above code the ordering of ax vector should be:

({ 1, 3, 6, 1, 2, 1, 2 })
({ 1, 3, 6, 1, 2, 1, 2, 1, 0 });
({ 1, 3, 6, 1, 2, 1, 2, 2, 3 });
({ 1, 3, 6, 1, 2, 1, 2,2,1, 3 });
({ 1, 3, 6, 1, 2, 1, 2,2,1, 4 });

I am unable to get what needs to be added in compare function to achieve it?