Boost multi-index based orderbook

As suggested here, I'm using Boost multi-index to implement orderbook. So far my code looks like this:

"CommonsNative.h" contains typedef int64_t myDecimal; and enum Side { Buy, Sell };

#pragma once

#include "CommonsNative.h"
#include <boost/multi_index_container.hpp>
#include <boost/multi_index/member.hpp>
#include <boost/multi_index/ordered_index.hpp>
#include <boost/multi_index/hashed_index.hpp>

using boost::multi_index_container;
using namespace boost::multi_index;

struct OrderBookItem {
    myDecimal price;
    int32_t lots;
    OrderBookItem(myDecimal price_) :price(price_), lots(0) {

    }
};

typedef multi_index_container
    <OrderBookItem, indexed_by<

    hashed_unique<
    BOOST_MULTI_INDEX_MEMBER(OrderBookItem,myDecimal,price)
    >,

    ordered_unique<
    BOOST_MULTI_INDEX_MEMBER(OrderBookItem,myDecimal,price),
    std::greater<myDecimal> /* sorted beginning with most frequent */
    >

    >> OrderBookContainer;

class OrderBook
{
public:
    OrderBook(void);
    ~OrderBook(void);
    void Add(Side side_, myDecimal price_, int lots_) 
    {
        if (side_ == Buy) {
            // inserts or returns existent
            OrderBookContainer::iterator it = buyContainer.insert(price_).first;
            // how to add lots i.e. OrderBookItem.lots += lots_?
            // auto curLevel = buyContainer.get<name>(price);
            // curLevel.lots += Lots;
        } else if (side_ == Sell) {
            // inserts or returns existent
            OrderBookContainer::iterator it = sellContainer.insert(price_).first;
        }
    }
private:
    OrderBookContainer buyContainer;
    OrderBookContainer sellContainer;
};

I have the following questions:

1. For here:

   OrderBookContainer::iterator it = buyContainer.insert(price_).first;
   

   If I already have an item with price = price_ I receive it in \$O(1)\$ (from hashtable). If such a level doesn't exist, then is it added in \$O(log n)\$? If I'm wrong, then what should I write to get an item if it exists (in \$O(1)\$) otherwise add it (in \$O(log n)\$)?

2. Once I have an item, how can I modify lots to something like this?

   OrderBookItem.lots += lots_