This flower is also known as Christ Plant. People used to believe that Jesus Christ was wearing a crown during crucifixion that was made from the thorny stem of this plant. This is a fleshy plant and has hard thorns around the stems. The stems are pliable and you can easily make a circle by blending it. The milky sap from the plant can cause irritation to skin, and its poisonous if ingested.
The pink flower that is seen at the photos are actually the transformed bracts of the flower. It holds the very tiny small yellow flower inside the dissembled bracts. This bract color can be red, pink, yellow, etc. This flower likes the sunlight, and that can effect to the brightness of the flower.
There are several variations of this flower is available around the world. Some botanists used to consider those as a separate species, some used to consider just as a variety from same species. Lets keep that argument apart for them. I haven't seen anything other than pink/rose in Bangladesh.
I don't know the exact Bengali(বাংলা) name of the flower, or Do I wonder whether there any Bengali(বাংলা) name really exists for this one! If I translate literally, then it will be Kontok Mukut(কন্টক মুকুট) in Bengali(বাংলা). This is a foreign plant at my country, originally this is native to Madagascar. You'll find more detail of this flower from WikiPedia. I have captured the images of this flower from Comilla(কুমিল্লা) during my travel at 2010.