What kind of Computer Data Structure is being used internally in a LDAP Database? Is it Binary Tree, B+ tree or Trei or something else?
It depends on which backend server you are using to service LDAP requests.
Microsoft Active Directory is using an evolution of the Exchange database as the backend. Novell eDirectory using the FLAIM database as the backend. Lotus Notes/Domino can service LDAP against its database structure. Oracle directory uses an Oracle DB in the backend (Go figure). OpenLDAP I am not sure. SunOne I am not sure.
LDAP remember is a protocol. Think about it this way, HTTP is a protocol, but the data could be stored on ext3, or on NFTS, or could be generated on the fly from a relational database, or it could even be some completely other device, such as in the case of a webcam. As a client, all you know is that you send HTTP requests and receive HTTP responses.
It would make sense if the underlying data store was itself a tree structure, but this can be done relationally with a self-join.