Kei roto ngā rākau i te wao.
There are trees in the forest.
'Wao' meaning 'forest' is an archaic term which comes from Te Wao Tapu Nui ā Tāne Mahuta - 'the great forest of Tāne Mahuta'.
This is a locative phrase which describes the location of something. A locative phrase is made up of:
A tense marker = Kei (present tense)
A location/locative noun = Roto (in)
A Subject = Rākau (tree) which is marked by a 'definite article' nga (the plural form of 'te' meaning 'the' which signifies the plural form of 'rākau' (trees)
An object marker = i
An object = Wao (Forest)