lock(num, user) {
        // it will just lock a node for a given user if it's not already locked THAT'S IT!
        if(this.treeHash[num]) return false;
        this.treeHash[num] = user;
        return true;
    }
Time O(1) | Space O(1)
@param {number} num 
@param {number} user
@return {boolean}