Hi Sudipto, 

Welcome to Box Community and glad to help! 

Box stores files and folders you place in the trash for a certain period of time, that default period is 30 days. Meanwhile, Please note that once deleted off of trash we are unable to support file recovery for our Free Individual plan. 

(https://support.box.com/hc/en-us/articles/360044196093-Managing-Trash)

Thanks for posting!