The Birth of Buddhism, in Sri Lanka, took place under the shade of a mango tree in 3rd Century BC.

King Devanampiyatissa and his minions were hunting deer, when he heard the calling of his name, which was followed by the radiant arrival of Arahant Mahinda Maha Thera and 6 others; almost supernaturally, in bright rays of light from atop a mountain.

Mahinda Thera wanted to preach Dharma to the King, but was not sure how intelligent the King was. Mahinda Thera asked, showing a nearby tree:

“What is the name of this tree?”
The King answered “This is a mango tree, Sir”
“Are there other mango trees other than this mango tree?”
“Yes. There are many other mango trees, Sir”
“Are there other trees beside this mango tree and other mango trees?”
“Yes. There are many other trees that are not mango trees, beside this mango tree and other mango trees, Sir”
“Are there any trees that are not other mango trees and any other trees”
“Yes. That is this mango tree, Sir”

“Do you have relatives?”
“Yes. I have many relatives”
“Are there people who are not your relatives?”
“Yes. There are many people who are not my relatives”
“Are there people other than your relatives and non relatives?”
“Yes. That would be me, Sir”
“Good. You are very intelligent and ready to listen to Buddha Dharma”

Then Mahinda Thera preached “Chula Hatthi Padopama Sutra” to the King.
By the end of the sutra, The King and his 40 thousand men became followers of Buddhism.

On the full moon day of June (today), devotees pay homage at the sacred site, Mihintale, and celebrate the Festival of Poson.