I'm really grateful for the elucidation of what tree a Simsapa is. Another candidate that I picked up from Sri Lanka is Murraya paniculata, a fragrant flowering shrub of South and South East Asia which many Sri Lankan monks told me corresponded with Simsapa. Worth considering all possibilities really but the above plant if it is the Simsapa, implies a fair familiarity by the Buddha of botany - gardens with this plant become highly fragrant at night as the flowers emit their perfume.