I am shown 79+ in Educational Codeforces Round 108 (Rated for Div. 2) but i get only 50+ after actual rating changes happen.

Why do programmers visualize/draw trees upside down? why root is not at the bottom?

Given an array consisting of integers and a number K. K<=10^9. How to get the number of subsequences that has a sum greater or equal to K. The array size can at most be 36.

Am i practicing in the right way? At least for the last 6-7 months I am trying to get better , I generally solve problems around 1500-1900(have solved 100+ problems within this range) , I try to up solve upto D or E , I try to do it without the help of editorial. I know most of the algorithms needed to solve upto D or E. But I still can't reach expert? How do I practice more efficiently? And codeforces is notthe only platform where i practice .