The unity of the Hadass:
The unity within the Hadass: The Hadass is only valid if it contains a majority of three leave sets that grow on the same line. This is unlike other leaves of a branch, in which the leaves grow in a scattered method, along the branch. This pattern followed by the leaves of the Hadass is the aspect of unity found in this branch, over that of other branches.
The representation of the Hadass within Jewry: The Midrash explains that the Hadass represents the people who spend their time performing Mitzvos and Gemilus Chassadim, but not learning Torah. Mitzvos correspond to the good smell found in the Hadass.
 Siddur Im Dach Shaar Halulav p. 264
 Vayikra Raba 30:12