I want to add c++ code of binary search tree

#### This issue is about [Binary Search Tree].

- [x] Issue Title is in form `Binary Search Tree [C++]`.
- [x] I searched or browsed the repo’s other issues to ensure this is not a duplicate.
- [x] This Algo/DS is worth adding to this repository.
- [x] Assign this issue to me (I want to work on this).
- [x] I ensure that I am not already assigned to 2 or more issues.
- [x] I will send my PR only after I'm assigned to this issue by any maintainer.
- [x] I understand that I will be unassigned from this issue if I fail to send a PR for this within a week.

Start by reviewing the repository’s existing algorithm and data-structure implementations to find the expected location and C++ conventions. Add a Binary Search Tree implementation in the matching style, then verify it against the repository’s available checks; no specific file or test is named in the issue.

Written by the indexing model from the issue text.