There is no way to visualize the decision tree from the model produced by Predict or Classify yet. However you can get some detailed information about the decision tree model as follows:
In[1]:= titanic=ResourceData["Sample Data: Titanic Survival"];
c=Classify[titanic->"SurvivalStatus",Method->"DecisionTree"]
Out[2]= ClassifierFunction[Input type: {Nominal,Numerical,Nominal}
Classes: died,survived ]
In[3]:= Information[c,"MethodOption"]
Out[3]= Method->{DecisionTree,DistributionSmoothing->1,FeatureFraction->1}
In[4]:= c[[1]]["Model"]
Out[4]= <|Tree->MachineLearning`DecisionTree[Number of nodes: 225
Number of leaves: 113],Processor->EmbedNominalVector\[ThinSpace]\[RightArrow]\[ThinSpace]MergeVectors\[ThinSpace]\[RightArrow]\[ThinSpace]Values,Calibrator->MachineLearning`CalibratorFunction[TemperatureScaling,<|Theta->0.462231|>],Method->DecisionTree,PostProcessor->Identity,Options-><|DistributionSmoothing-><|Value->1,Options-><||>|>,FeatureFraction-><|Value->1,Options-><||>|>|>|>
In[5]:= c[[1]]["Model"]["Tree"]//FullForm
Out[5]//FullForm= MachineLearning`DecisionTree[Association[Rule["FeatureIndices",NumericArray[List[1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,3,3,3,3,3,3,3,3,3,3,3,3,3,3,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,6,6,6,6,6,6,6,6,6,6,6],"Integer16"]],Rule["NumericalThresholds",List[-1.1093288462606128`,-1.09195429877913`,-1.0851267088215946`,-1.0215090313921906`,-0.9933393992363942`,0.05578158707301903`,0.06349617385960019`,0.10698518650736097`,0.1438680732723027`,1.1244347232941254`,1.129311963025544`,1.1409925716270861`,1.15777655085511`,1.1587633392580745`,1.171232551579825`,1.1853282036306936`,1.1884314762737993`,1.1982708136799285`,1.1986830729887432`,1.2049541955720044`,1.2138669812231202`,1.2333737225205454`,1.236920699175986`,1.2478166559325916`,1.2631421784212422`,-0.6521623222004684`,-0.6521622295408744`,-0.6521620242386478`,-0.6521614585949597`,-0.2030572009451387`,-0.2030570377237761`,-0.2030568866336571`,-0.20305687163865116`,-0.20305567453469475`,0.09869252461898023`,0.09869258425986824`,0.09869280222533691`,0.09869314297553534`,0.09869319931483313`,0.09869334503472878`,0.09869336303013855`,0.09869368571235419`,0.09869371251476487`,0.09869380755036536`,0.09869415456637161`,0.09869424883269172`,0.0986943357839214`,-0.4474913175797399`,-0.4474912970155966`,-0.44749107051057185`,-0.4474909202360258`,-0.44749072029312253`,-0.44749061010480323`,-0.44748981363609325`,-0.44748980211170947`,0.08446763612574955`,0.0844677320775505`,0.08446790266898689`,0.08446834154121462`,0.3972744078903446`,0.3972755238204073`,-0.5700892529280701`,-0.5700891448269508`,-0.5700888172353218`,-0.5700887791484793`,-0.5700886427694413`,-0.5700884122166382`,-0.570088108842751`,-0.570088095932906`,-0.5700879219241077`,-0.57008740072637`,0.3058445670476174`,0.30584481890947207`,0.30584529998720517`,0.3058456072587361`,0.3058456162007218`,0.30584584608112214`,0.305845931628907`,1.0462073237997662`,1.04620740639019`,1.0462074099182053`,1.0462087429290876`,-0.2859567735059471`,-0.2859564694186271`,-0.2859563025212852`,-0.2859562800495861`,-0.2859558419383742`,-0.285955792484437`,-0.2859552341329527`,-0.2859550904184345`,-0.2859548527481892`,-0.28595478781779243`,0.17642749014618417`,0.1764279660974715`,0.17642797433799567`,0.17642797520252884`,0.17642838872232613`,0.1764284324942041`,0.17642849330162316`,0.17642893372111212`,0.17642894339225756`,-0.3600153563844246`,-0.3600152647924192`,-0.3600147157403142`,-0.3600135110979804`,-0.36001340559709355`,-0.003911936948213508`,-0.003910764595476518`,-0.003910548793407916`,-0.00391051413862169`,-0.003910428801723417`,-0.00391020447817348`]],Rule["NominalSplits",List[]],Rule["Children",NumericArray[List[List[-7,-8],List[1,76],List[36,71],List[-91,95],List[70,88],List[45,49],List[-36,-37],List[-39,-40],List[-50,-51],List[106,90],List[-111,17],List[-78,-79],List[12,-54],List[10,47],List[-44,-45],List[-58,-59],List[-112,-113],List[67,87],List[-87,-88],List[-101,-102],List[56,-13],List[-55,-56],List[34,59],List[-41,-42],List[68,-100],List[105,-75],List[104,29],List[26,91],List[-98,-99],List[9,-35],List[20,-90],List[-6,21],List[-27,-28],List[-29,8],List[82,55],List[51,2],List[-81,-82],List[93,6],List[107,46],List[-92,-93],List[50,-48],List[40,-84],List[-52,-53],List[-61,-62],List[112,108],List[101,-21],List[77,89],List[-85,-86],List[15,97],List[-70,-71],List[-2,-3],List[75,42],List[-63,-64],List[98,-31],List[99,-1],List[-17,-18],List[33,-16],List[57,23],List[-30,24],List[103,69],List[-72,-73],List[-4,102],List[-14,5],List[-38,16],List[-49,61],List[64,-26],List[84,-94],List[-108,11],List[18,27],List[65,-34],List[62,83],List[-67,-68],List[43,13],List[72,100],List[-83,4],List[-9,-10],List[-23,78],List[22,80],List[31,-80],List[79,-57],List[96,58],List[81,32],List[-5,14],List[-105,86],List[-106,-107],List[-109,-110],List[-95,-96],List[60,28],List[-24,-25],List[73,-22],List[-76,-77],List[3,35],List[-19,54],List[66,-15],List[-103,-104],List[94,-12],List[-46,-47],List[109,-43],List[38,39],List[48,-69],List[74,41],List[-11,63],List[-74,19],List[85,-97],List[25,-89],List[30,7],List[-20,111],List[53,110],List[-60,37],List[-65,-66],List[-32,-33],List[52,44]],"Integer16"]],Rule["LeafValues",NumericArray[List[List[11,1],List[2,2],List[1,15],List[1,3],List[3,5],List[4,1],List[2,2],List[8,1],List[1,5],List[4,1],List[1,3],List[1,86],List[2,1],List[12,1],List[2,1],List[4,1],List[2,2],List[1,9],List[3,1],List[1,3],List[6,1],List[1,5],List[55,1],List[4,1],List[1,2],List[1,26],List[2,2],List[1,10],List[1,28],List[1,3],List[2,1],List[16,1],List[3,2],List[1,6],List[338,43],List[1,3],List[3,1],List[1,12],List[1,6],List[2,2],List[3,1],List[1,2],List[2,1],List[1,4],List[2,1],List[15,1],List[1,2],List[1,10],List[1,3],List[4,1],List[1,3],List[1,3],List[2,1],List[1,2],List[1,3],List[3,1],List[39,1],List[3,1],List[1,2],List[1,18],List[1,5],List[2,1],List[1,10],List[2,2],List[4,1],List[1,3],List[3,1],List[1,5],List[1,2],List[3,1],List[1,4],List[7,1],Lis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