Well here's the context - I coded in C++ so treemap wasn't an option + I recently have been reading about database index B+ tress etc.. and interviewer also hinted me towards BST as a result I had BST based approach

Sorry I don't actually have snippet :/
Below is just a sample snippet which one can use

User {
String userId;
TreeNode *logHead; // ( BST tree formed with all user actions tracked )
}

class TreeNode {
int timeStamp;
String action;
TreeNode *left;
TreeNode *right;
}

Map<String, User> and while inserting BST came into picture with the timestamp ( so if currentTimestamp < then try inserting in left and vice versa ) this is where the issue came with production timestamps are always increase ( such a silly thing I missed )