According to Hinduism which trees are sacred and why?

Types of trees are often mentioned by name in Hindu stories.

This gives them associations with the gods who played the major roles in those stories.

As a few examples...

The Ashoka tree represents love and harmony. Incidentally, Siddartha the Buddha was born under one, so it is the holy tree of Buddhism as well.

The Banyan tree is the sacred plant of Lord Vishnu.

The Bael tree is the sacred plant of Lord Shiva.

The Neem tree is associated with the goddess Durga.