1. A method for decoding a bitstream for a video signal, the method comprising: deriving at least one motion vector candidate from at least one neighboring block of a current block; constructing a motion vector candidate group of the current block, the motion vector candidate group comprising a plurality of motion vector candidates including the derived at least one motion vector candidate; obtaining a motion vector predictor of the current block from the constructed motion vector candidate group; and decoding the current block based on the motion vector predictor, wherein the deriving the at least one motion vector candidate includes: selecting a motion vector of the at least one neighboring block as the at least one motion vector candidate when a first reference picture list is used for the current block, a second reference picture list different from the first reference picture list is used for the at least one neighboring block, and a reference picture of the current block in the first reference picture list has a same picture order count (POC) value as a reference picture of the at least one neighboring block in the second reference picture list.