וַיְזַבֵּ֧חַ וַיְקַטֵּ֛ר בַּבָּמ֖וֹת וְעַל־הַגְּבָע֑וֹת וְתַ֖חַת כָּל־עֵ֥ץ רַעֲנָֽן׃
And he sacrificed and offered in the high places, and on the hills, and under every leafy tree.
Read midrashic interpretation of II Kings 16:4: and classical rabbinic exegesis.