How to gather column values after complex pandas aggregation

I perform some non-trivial aggregation as in the following:

aggregations = {
    'x_TmId': { 
        'Trays': 'nunique',  
        'Orderlines': 'count', 
    },
    'x_Qty': 'sum'
}

  newdf = pick.groupby(['Date','x_OrderId']).agg(aggregations).reset_index(True)

at this point the aggregated dataframe columns can be called as usual by

  newdf.columns

but that returns something I did not encounter before: a MultiIndex object:

MultiIndex(levels=[['x_TmId', 'x_Qty', 'x_OrderId'], ['Orderlines', 'Trays', 'sum', '']],
           labels=[[2, 0, 0, 1], [3, 0, 1, 2]])

At this point, I realize I don't know how to call as example the new variables "sum"? There must be some similar question on stackoverflow, but could not find it yet.