Is there a data structure which performs O(1) or O(logn) insertion at back and same for removal and we can find the number of elements less than K (any particular element ) in O(logn) if the data structure is already sorted (means binary search is applicable )
Order Statistics Tree. You can get the order of the element and it's the number of elements less than it. Order, deletion and insertion take O(log n) time. Here's its Wiki article
You could certainly do that with a treap, just store keys along with subtree sizes.
Like this, for example
If you need k-th smallest element, just write a split on sizes instead of keys.