Malbim: The end of the dream - being fettered, eating grass and living with Chayos, does not apply to a tree, rather, to a person. This is not part of the dream, rather, its interpretation. Cutting the tree hints to lunacy, becoming an animal and removal from kingship. Chazal said that repetition of a dream shows that it will be fulfilled soon ¹ . We could have said that the first dream can mean that his kingship will be totally nullified, and later sprout from its roots, i.e. his sons, like "v'Yatza Choter mi'Geza Yishai v'Netzer mi'Sharashav Yifreh", i.e. via his seed. However, the second dream, which compared him to an animal, shows that it will be fulfilled via him - he will return to his kingship.

Malbim: The decree is decided and imminent.

Rashi: This came to my master, the king.

Malbim: All will be fulfilled in the king (not via his seed), like he explains.