Statements:
No tree is a flower 

Some trees are fruits

Conclusions:
(I) Fruits that are trees are not flowers.

(II) No fruit is a flower.

Conclusion (I): Fruits that are trees are not flowers.

We know from (2) that some trees are fruits.

From (1), no tree can be a flower.

So, those fruits that are trees definitely cannot be flowers. Hence, Conclusion I follows.

Conclusion (II): No fruit is a flower.

We have no statement that directly links fruits and flowers.

Fruits can still be flowers or not — It is not certain. Hence, conclusion II does not follow.