- Session 17 is blocking session 26 from updating a row in the test_row_lock table as it currently holds a lock on that row. - Session 1 inserted a row into the test_unique_insert_row_lock table and is blocking session 36 from inserting a duplicate value into the same table until session 1 commits. - Lock trees in Oracle represent multiple sessions waiting to acquire the same row lock, with sessions lower in the tree waiting on those above it.