Condenses two molecules of dimethylallyl diphosphate (DMAPP) to produce mainly an irregular monoterpene, chrysanthemyl diphosphate (CPP) and lower amounts of a branched monoterpene, lavandulyl diphosphate (LPP). CPP is a precursor of the pyrethrin insecticides. When incubated with isopentenyl diphosphate (IPP) and DMAPP, catalyzes three competing isoprenoid condensation reactions, a chain elongation to give geranyl diphosphate (GPP), a cyclopropanation to give CPP and a branching to give LPP. dimethylallyl diphosphate + isopentenyl diphosphate = (2E)-geranyl diphosphate + diphosphate 2 dimethylallyl diphosphate = (R,R)-chrysanthemyl diphosphate + diphosphate 2 dimethylallyl diphosphate = (R)-lavandulyl diphosphate + diphosphate Binds Mg(2+) or Mn(2+). The Asp-Asp-Xaa-Xaa-Asp/Glu (DDXXD/E) motif is important for the catalytic activity, presumably through binding to Mg(2+). Belongs to the FPP/GGPP synthase family.