Sundarbans are named after these trees

Hint: Sundarbans is a mangrove area in the Bay of Bengal delta formed by the confluence of the Ganges, Brahmaputra, and Meghna Rivers. It runs from the Hooghly River in West Bengal, India, to the Baleswar River in Bangladesh.

Complete answer:
The name Sundarbans is thought to be derived from sundri or sundari, the name of the large mangrove trees found in the area. The forestland gives way to a low-lying mangrove swamp near the coast, which is made up of dunes and mudflats.

Mangrove forests cover roughly two-fifths of the total surface area of the Sundarbans region, with water covering roughly half of that area. The erosional forces of the sea and wind along the coast, as well as the massive loads of silt and other sediments deposited along the numerous estuaries, are constantly transforming the landscape.

Human activity has also altered the landscape, most notably by removing forests, which hastens erosion. Furthermore, because large amounts of river water have been diverted upstream for irrigation and other purposes, salinity in the mangrove swamps has moved further inland, particularly in the Indian sector of the territory.

The Sundarbans are home to several reptile and amphibian species, including crocodiles, Indian pythons, cobras, and marine turtles. More than 250 bird species, both seasonal migrants and permanent residents, live in the region, including hornbills, storks, and other waders, kingfishers, white ibis, and raptors such as sea eagles.
Thus, The Sundarbans are named after the Sundari trees.

Note: Heritiera fomes is a type of mangrove tree in the Malvaceae family. It is also known as sunder, sundri, jekanazo, and pine kanazo. It is the dominant mangrove tree species in Bangladesh and India's Sundarbans, accounting for roughly 70% of the trees in the area.