Complex sentence: The Parliament was established by the British New Zealand Constitution Act 1852 which established a bicameral legislature, but the upper house, the Legislative Council, was abolished in 1951 so the legislature is now unicameral.
Split into simpler sentences: The Parliament was established by the British New Zealand Constitution Act 1852 which established a bicameral legislature. The upper house, the Legislative Council, was abolished in 1951 so the legislature is now unicameral.