The male flower of the White mulberry (Morus alba) is catkin like spike inflorescence. The flowers appear in mid spring from late March to mid-May (depending on your latitude).
As can be seen from the image below the male flowers appear on the tree before the new leaves.
below - new leaves on the male tree (male and female are separate trees)
The images above and below are of the flowers of the female White mulberry tree. The female flowers are shorter than their male counterparts.