大般涅槃經集解 3.6

3.6

案僧亮曰：去地七多羅樹者，彼以豪族自憍，不願雜坐，故置之空也。

Sengliang states: "Regarding their being 'seven tāla trees above the ground': because they were haughty on account of their noble clanship and did not wish to sit mingled together, they were placed in the sky."