Hebrew: bakah, “to weep;” rendered “Baca” (Revised King James Version, “weeping”) in Psalms 84:6
The plural form of the Hebrew bekaim is rendered “mulberry trees” in 2 Samuel 5:23-24 and 1 Chronicles 14:14-15. The tree here alluded to was probably the aspen or trembling poplar.
“We know with certainty that the black poplar, the aspen, and the Lombardy poplar grew in Palestine [Israel]. The aspen, whose long leaf-stalks cause the leaves to tremble with every breath of wind, unites with the willow and the oak to overshadow the watercourses of the Lebanon, and with the oleander and the acacia to adorn the ravines of Southern Palestine” (Kitto).
By “the sound of a going in the tops of the mulberry trees” we are to understand a rustling among the trees like the marching of an army. This was the signal that the Lord himself would lead forth David's army to victory.