basic question- deciding index type

guy 1: a table has 10,00000 db blocks
guy 1: it has 9999999999 rows
guy 2: vempires r on the floor
guy 1: on column productid there are 23 distinct values
guy 1: what index would u prefer
guy 2: b+tree
guy 1: nope
guy 1: this column has very high cardinality
guy 2: k
guy 2: sir
guy 1: this column has very few distinct values as comparing to the number of rows in table
guy 1: so very less selectivity . if it was highly selctive only then b+tree
guy 2: yup
guy 1: column seems good candidate for for bmp index
guy 2: im recalling
guy 1: but if heavy dml then even bmp index is also avoided
guy 2: its good .commender
guy 1: because it locks segments (actallyu exents) of objects
guy 2: k
guy 1: so no index if heavy dml on above
guy 2: k