from yt.analysis_modules.halo_merger_tree.api import *
mtc = MergerTreeConnect(database='halos.db')

line = "SELECT * FROM Halos WHERE HaloMass > 1.0e7 and HaloMass < 1.0e8 and SnapCurrentTimeIdentifier=1395408982;"

results = mtc.query(line)

halolist = [x[0] for x in results]
halolist = halolist[:10]

MergerTreeDotOutput(halos=halolist,database='halos.db',dotfile='MergerTree.gv',link_min=0.7)