def __init__(self, field_mask=None):
    self._root = {}
    if field_mask:
      self.MergeFromFieldMask(field_mask)
Initializes the tree by FieldMask.
dataset/ETHPy150Open GoogleCloudPlatform/python-compat-runtime/appengine-compat/exported_appengine_sdk/google/net/proto2/python/internal/well_known_types.py/_FieldMaskTree.__init__