Bilva tree is sacred to Lord Shiva.

Just like the way Tulsi plant is sacred to Lord Krishna/ Vishnu and Durva grass is sacred to Lord Ganesha, Bilva tree is sacred to Lord Shiva. Since the Bilva leaf has such significance in the worship of Shiva, it is common to find Bilva trees cultivated in the vicinity of Shiva temples. According to Shiva Purana, the Bilva tree is the manifest form of Shiva himself, while all the great tirthas are said to reside at its base. One who worships the ShivaLingam while sitting under the Bilva tree attains the highest bliss of oneness with Shiva. He who pours water over his head at the root of a bilva can be considered to have taken his bath at places of pilgrimages. One who performs Bilva pooja with flowers and incense achieves Shiva loka, the abode of pure consciousness, and has happiness and prosperity bestowed upon them. The lighting of the deepak before this tree bestows knowledge and enables the devotee to merge in Shiva. The Shiva Purana also claims that if the devotee removes the new leaves from one of the branches of that tree and worships the tree with them, they will be freed from vice, One who feeds a devotee under the Bilva will grow in virtue. For Happiness and Prosperity – Perform Bilva Pooja with flowers and incense. For Supreme Knowledge Light deepak before Bilva tree. For Freedom from Vice – Remove new leaves from one of the branches of Bilva tree and worship the tree with them. For Growth of Virtue – Feed a Shiva devotee under the Bilva.
Love, Light & Blessings ~ Om Namah Shivaya ~ Jai Shiva Shankar!