Semi Puja Story of Dasara, Semi Pooja katha, Story of Jammi tree (Shami Vruksha)
Pandavas lost their kingdom and every thing to the Kauravas in gambling. Finally Kauravas agreed to return the kingdom of Pandava along with their wealth if they lived in a forest for 12 years and after that they should lead a secret life for one year. In the one year if they are found as Pandavas, and Kauravas were able to recognize them then they have to repeat the stay in the forest as well as the secret life of one year and this would continue until they were not recognized by the Kauravas during the secret period.
This secret period was called as Agyat Vaas. After completing the 12 years Pandavas were getting ready for the Agyat Vas. The thing that worried them the most was where to hide the weapons that were presented by the Gods. They cannot trust anyone and had to hide the weapons, such that they do not fall into the wrong hands.
They finally concluded to hide the weapons on a Shami tree or Jammi Chettu. They concealed the weapons and prayed to the Shami tree. They asked the Shami tree to show the weapons as a dead corpse to anyone who see them and as weapons to Pandavas only. Thus the Shami tree was worshipped by the Pandavas for protecting their weapons. On the day of Vijaya Dashami or Dasara, Pandavas prayed to the Shami tree and got back their weapons. Hence it has become a tradition to pray to the Shami tree on Dasara.
In some places Simolanghana (seema + Ullanghana) is done. Which means crossing the border and entering the enemy state for war. Before Simolanghana is done Shami tree is prayed and the territory of the enemy is entered. Now a days the outskirt of the village or town is crossed symbolically.