varea_stack

from bokeh.models import ColumnDataSource
from bokeh.plotting import figure, show

source = ColumnDataSource(data=dict(
    x=[1, 2, 3, 4, 5],
    y1=[1, 2, 4, 3, 4],
    y2=[1, 4, 2, 2, 3],
))
p = figure(width=400, height=400)

p.varea_stack(['y1', 'y2'], x='x', color=("grey", "lightgrey"), source=source)

show(p)