Consider evaluating an expression like "col1 + col2 == col3"

A tree based evaluator has to do something like -

    for (int i = 0; i < df.size(); i++) {
        // switch on expression type (column, binary operator, unary operator etc)
        // switch on expression operator type (add, subtract, equals etc)
        // switch on column type (int, long, float etc)
        // actual evaluation
    }

whereas a bytecode based evaluator is able to run something equivalent to -

    for (int i = 0; i < df.size(); i++) {
        result[i] = df.getLong(column1Index, i) + df.getLong(column2Index, i)) == df.getLong(column3Index, i)
    }