I think nakul is indirectly challenging Abhi to win over simi. He was telling simi that he used to keep a gift on the top of the tree so that abhi could climb and take it, in that way he will learn to climb the tree also.
I think what he ment was if Abhi wants simi, he should try very hard and he should show his worthiness, then only he will get simi, till then he will hold on to her 😕 or be near sethi parivaar