The tree of life/central pillar/axis mundi is a very important both archaic and universal symbol for comparing different religions according to the leading authority within this field - Mircea Eliade. In short it's the center of the world, the connection point between the heaven (where "the Sacred" reside), the earth (humans) and often the underworld. Compare Jacob's ladder, Gunungan etc.
Seeing the scales/eggs as clouds, symbolising heaven, is maybe a key to this riddle?
On the "figures" inbetween an interpretation could be that they somehow represents something dualistic, like + - + -.
To have an idea what it could be of course you have to know more about the local myths and beliefs than I do at the moment. Maybe if somebody knows something about local creation myths a theory could be developed? An example could be if f.i. at the time of creation some divine force created two men and two females from where all humans origin?
Not knowing if this is the case a hypothesis of this inlay as talismanic could be:
At the base of the Kris (heaven, the Sacred?) is something of a "battery/power source" that transmits some kind of energy (the + - + -). This energy is transformed into a (earth - vegetative, creative) force (birth-life-death) that is pointed at an enemy in battle to powercharge this Kris.
If the + - + - represents male and female ancestors then we have a metaphysical "nuclear missile launcher"?
Michael